EX-5.1

Exhibit 5.1

October 31, 2018

Aflac Incorporated

1932 Wynnton Road

Columbus, Georgia 31999

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 $550,000,000 aggregate principal amount of its 4.750% Senior Notes due 2049 (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 October 29, 2018 (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 an eighteenth supplemental indenture, dated as of October 31, 2018 (the “Eighteenth Supplemental Indenture,” and together with the Base Indenture, the “Indenture”), between the Company and the Trustee. 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 resolutions of the Executive Committee of the Board of Directors adopted on October 23, 2018, 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 deemed necessary or appropriate as a basis for the opinions set forth below. In my examination, I have assumed the legal capacity of all natural persons, the genuineness of all signatures, the authenticity of all documents submitted to me as originals, the conformity to original documents of all documents submitted to me as facsimile, electronic, certified or photostatic copies, and the authenticity of the originals of such copies. I have also made such other investigation as I have deemed appropriate.

Based upon the foregoing, I am of the opinion that:

1. The Company has been duly incorporated and is validly existing as a corporation in good standing under the laws of the State of Georgia, with the corporate power and authority to execute and deliver the Indenture and the Notes.