EX-5.1

Exhibit 5.1

LOGO

Audrey Boone Tillman, Esq.

Executive Vice President & General Counsel

Re: Aflac Incorporated Registration Statement on Form S-3

Ladies and Gentlemen:

I am the Executive Vice President and General Counsel to Aflac Incorporated, a Georgia corporation (the “Company”), and as such have acted as counsel for the Company in connection with the registration of (i) ¥12,600,000,000 aggregate principal amount of its 0.500% Senior Notes due 2029 (the “2029 Notes”), (ii) ¥9,300,000,000 aggregate principal amount of its 0.843% Senior Notes due 2031 (the “2031 Notes”), (iii) ¥9,800,000,000 aggregate principal amount of its 0.934% Senior Notes due 2034 (the “2034 Notes”), and (iv) ¥6,300,000,000 aggregate principal amount of its 1.122% Senior Notes due 2039 (the “2039 Notes,” and together with the 2029 Notes, the 2031 Notes, and the 2034 Notes, the “Notes”) under a Registration Statement on Form S-3 (333-227244) filed on September 7, 2018 with the Securities and Exchange Commission under the Securities Act of 1933, as amended (the “Securities Act”). The Notes were offered for sale pursuant to the base prospectus accompanying the Registration Statement, as supplemented by a prospectus supplement relating to the Notes dated December 11, 2019 (the base prospectus, the prospectus supplement and any amendments thereto, collectively, the “Prospectus”). The Notes are to be issued under an indenture, dated as of May 21, 2009 (the “Base Indenture”), between the Company, as issuer, and The Bank of New York Mellon Trust Company, N.A., as trustee (the “Trustee”), as supplemented by (i) a Nineteenth Supplemental Indenture, dated as of December 17, 2019 (the “Nineteenth Supplemental Indenture”), between the Company and the Trustee, in the case of the 2029 Notes, (ii) a Twentieth Supplemental Indenture, dated as of December 17, 2019 (the “Twentieth Supplemental Indenture”), between the Company and the Trustee, in the case of the 2031 Notes, (iii) a Twenty-First Supplemental Indenture, dated as of December 17, 2019 (the “Twenty-First Supplemental Indenture”), between the Company and the Trustee, in the case of the 2034 Notes, and (iv) a Twenty-Second Supplemental Indenture, dated as of December 17, 2019 (the “Twenty-Second Supplemental Indenture”), between the Company and Trustee, in the case of the 2039 Notes. As used herein, the term “Indenture” means the Base Indenture as supplemented by (i) in the case of the 2029 Notes, the Nineteenth Supplemental Indenture, (ii) in the case of the 2031 Notes, the Twentieth Supplemental Indenture, (iii) in the case of the 2034 Notes, the Twenty-First Supplemental Indenture, and (iv) in the case of the 2039 Notes, the Twenty-Second Supplemental Indenture.

This opinion is being furnished in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Securities Act.

In connection with rendering the opinions set forth below, I, or attorneys under my supervision, have examined the Registration Statement, the Prospectus contained therein, the Indenture, the Articles of Incorporation of the Company, as certified by the Secretary of State of the State of Georgia, the Bylaws of the Company, as certified by J. Matthew Loudermilk, Corporate Secretary of the Company, resolutions of the Board of Directors of the Company adopted on August 14, 2018 and November 12, 2019, as certified by J. Matthew Loudermilk, Corporate Secretary of the Company. I have also examined originals or copies, certified or otherwise identified to our satisfaction, of such records of the Company and such agreements, certificates and receipts of public officials, certificates of officers or other representatives of the Company and others, and such other documents as I have