An absorbent article having side flaps that can expand/contract, wherein an occurrence in which a back side end section falls to a non-skin side is suppressed, and leakage of excrement from the back is prevented. An absorbent article (1) comprises: an absorbent main body (AB) that includes an absorbent body (4)； and a pair of side flaps (SF, SF) that extend to outer sides from both width direction end sections of the absorbent main body. The side flaps each comprise a sheet-shaped expansion/contraction member (12) that can expand/contract in the width direction, sheet members (7a, 7b) that are respectively laminated to both thickness direction surfaces of the expansion/contraction member, and a securing member (8) that is connected to a width direction outside end section of the expansion/contraction member and extends to an outer side. Each of the pair of side flaps is bonded further toward a skin side, in the thickness direction, than the absorbent main body. In a length direction, a back side end section of the absorbent body is positioned further toward the back side than an imaginary line that connects, in the width direction, belly side end edges of the securing members.
