Disclosed is a diaper (1A) comprising: an absorbent main body (2) which comprises at least a liquid-permeable top sheet (3), a liquid-impermeable back sheet (4) and an absorbent body (5) which is disposed between the top sheet and the back sheet for the purpose of absorbing and retaining liquid, and which has a back side region (S1), a crotch region (S2) and a front side region (S3) in the longitudinal direction L running from the back side Ba to the front side Fr when the nappy is being worn; and a pair of left and right side flap parts (10) which are provided on both sides of the absorbent main body (2) in the width direction W, wherein a front side extension region (15) which extends around the waist is provided in the front side region (S3) of each of the side flap parts (10).