Major Shareholder Reports 0.41pp Stake Increase to 54.61% via Open-Market Purchases

Report on Mass Holding of Stocks (General) Version 6.0 Cheonbo Co., Ltd. Report on Mass Holding of Stocks (General format: For reports under Article 147 of the Financial Investment Services and Capital Markets Act where the purpose is 'to influence management control') To: Financial Services Commission Date of reporting obligation: June 19, 2026 To: Korea Exchange Report preparation reference date: June 19, 2026 Reporter: Lee Sang-ryul === Summary Information === Issuer: Cheonbo Co., Ltd. Relationship with issuer: Largest shareholder Report category: Change Number and ratio of shares held: - Previous report: 7,938,704 shares (54.20%) - Current report: 7,998,894 shares (54.61%) Major contracted shares and ratio: - Previous report: - - Current report: - Number and ratio of voting rights: - Previous report: 5,543,093 (45.24%) - Current report: 5,603,283 (45.73%) Major contracted voting rights and ratio: - Previous report: - - Current report: - Reason for reporting: - Largest shareholder share purchase - Special-related person share purchase * The reporter confirms that the holding status of the reporter and special-related parties as of the reference date has been accurately prepared in accordance with relevant laws and notes, with no false statements or omissions of material matters. === Part 1: Report Overview === 1. Issuer Information - Company name: Cheonbo Co., Ltd. - Company code: 278280 - Corporate classification: KOSDAQ-listed corporation - Total voting shares issued: 12,253,025 2. Major Holder Information A. Reporter (1) Overview - Report category: Change - Joint reporting - Reporter classification: Individual (domestic) - Nationality: Republic of Korea - Name: Lee Sang-ryul (李相律 / LEE SANG RYUL) - Address: Jungangtap-myeon, Chungju-si, Chungcheongbuk-do - Date of birth: 1961-10-21 - Occupation: Representative Director of Cheonbo Co., Ltd. - Relationship with issuer: Largest shareholder - Business contact: Yoon Hong-hwan, Assistant Manager, Management Team, Cheonbo Co., Ltd. B. Special-Related Parties (14 persons/entities) 1. Seo Ja-won — Individual (domestic), Representative Director, Major shareholder, Chungju 2. Lee Seul-ji — Individual (domestic), Relative, Shareholder, Seoul Gangnam 3. Lee Hyun-ji — Individual (domestic), Relative, Shareholder, Chungju 4. Lee Young-seok — Individual (domestic), Relative, Shareholder, Chungju 5. Choi Byung-min — Individual (domestic), Relative, Shareholder, Suwon 6. Shin Soo-il — Individual (domestic), Relative, Shareholder, Siheung 7. Lee Sang-eun — Individual (domestic), Relative, Shareholder, Chungju 8. Joo Hye-shin — Individual (domestic), Relative, Shareholder, Anyang 9. Joo Hye-yeon — Individual (domestic), Relative, Shareholder, Anyang 10. Lee Woon-jong — Individual (domestic), Relative, Shareholder, Hwaseong 11. Cheonbo Precision — Domestic corporation, Affiliate, Eumseong 12. Solique Investment — Domestic corporation, Affiliate, Seoul Gangnam 13. Woo Dong-hee — Individual (domestic), Executive (Registered) 14. Lee Geun-pil — Individual (domestic), Executive (Registered) (2) Specifics for corporate special-related parties (KRW million): Cheonbo Precision Co., Ltd. - Legal form: Corporation - Total assets: 35,446 - Total liabilities: 9,305 - Total equity: 26,141 - Capital: 200 - Representative: Lee Sang-ryul - Decision body: Shareholders' meeting, Board - Largest shareholder: Lee Sang-ryul (47.5%) Solique Investment Co., Ltd. - Legal form: Corporation - Total assets: 22,394 - Total liabilities: 32 - Total equity: 22,362 - Capital: 20,000 - Representative: Ryu Si-myung - Decision body: Shareholders' meeting, Board - Largest shareholder: Cheonbo Precision (50.9%) C. Collective Investment Manager: N/A 3. Number and Ratio of Shares Held - Previous report (June 12, 2026): Lee Sang-ryul + 14 special-related parties; 7,938,704 stock-equivalents (54.20%); 5,543,093 voting shares (45.24%) - Current report (June 19, 2026): Same parties; 7,998,894 stock-equivalents (54.61%); 5,603,283 voting shares (45.73%) - Change: +60,190 shares (+0.41pp stock-equivalents); +60,190 voting shares (+0.49pp); total voting shares outstanding unchanged at 12,253,025 4. Purpose of Holding: To influence management control, including: 1) Appointment/dismissal of directors and auditors or suspension of duties 2) Amendment of articles related to corporate organs such as the board 3) Changes to capital 4) Decision on dividends 5) Mergers, divisions, and division-mergers 6) Comprehensive share swaps and transfers 7) Acquisition or transfer of entire business or material portions thereof as specified by the FSC 8) Disposal of all assets or material portions as specified by the FSC 9) Lease of all business, delegation of management, profit-sharing contracts, etc. 10) Dissolution of the company The reporter is exercising de facto influence over the above matters. 5. Reason for Change - Change method: Largest shareholder share purchase; Special-related person share purchase - Reason: Stock price stabilization and enhancement of shareholder value === Part 2: Mass Holding Details === 1. Holdings by Reporter and Special-Related Parties A. By type of share - Lee Sang-ryul (Reporter): 3,339,720 common shares + 958,244 convertible/other = 4,297,964 (29.34%) - Seo Ja-won: 1,037,065 shares (7.08%) - Lee Seul-ji: 535,000 shares + 287,474 other = 822,474 (5.61%) - Lee Hyun-ji: 515,000 shares + 958,244 other = 1,473,244 (10.06%) - Lee Young-seok: 12,580 shares (0.09%) - Choi Byung-min: [Translation truncated]