This underwear-type absorbent article (1) is equipped with a stomach-side sheet member (2A), a back-side sheet member (2B) and an absorbent main body (3) affixed bridging therebetween. The stomach-side sheet member (2A) and the back-side sheet member (2B) each have an extension section (21a, 21b) and a main body section (20a, 20b) that expand/contract in the diaper-width direction. When the extension section (21b) of the back-side sheet member (2B) is divided into an upper back-side extension section (B4) and a lower back-side extension section (B5), the upper back-side extension section (B4) and the portion of the stomach-side sheet member corresponding to the upper back-side extension section (B4) have a contraction stress in the direction of article width per unit length in the direction of article length that is greater than the same contraction stress of the lower back-side extension section (B5).
