A disposable diaper (1) comprising: an absorbent main body (2) including an absorbent body (23), a skin-side sheet (21) arranged on the inner surface side of the absorbent body, and a non-skin-side sheet (22) arranged on the outer surface side of the absorbent body and an expanding/contracting side panel (3) attached to a side section of the absorbent main body. The side panel (3) has: a fastening tape (4) provided at the tip section thereof two sheets (31, 32) and an elastic member (33) fixed therebetween and a main body-side adhesive layer (35) fixing an end section on the absorbent main body (2) side of the elastic member (33), or the vicinity thereof, and a tip-side adhesive layer (36) fixing an end section on the tip section (3a) side of the side panel of the elastic member (33), or the vicinity thereof. The side panel (3) has an upper side joining section (66) wherein the sheet (31) arranged on the inner surface side and the skin-side sheet (21) are joined. The upper side joining section (66) and the main body-side adhesive layer (35) overlap in the diaper thickness direction.本發明之拋棄式尿布(1)包括：吸收性本體(2)，其包含吸收體(23)、配置於吸收體之內表面側之肌膚側片材(21)及配置於吸收體之外表面側之非肌膚側片材(22)；及伸縮性之側片(3)，其安裝於吸收性本體之側部；側片(3)於前端部設置有黏扣帶(4)，且包含2片片材(31、32)及固定於其間之彈性構件(33)，且包含固定彈性構件(33)之吸收性本體(2)側之端部或其附近的本體側接著劑層(35)、及固定彈性構件(33)之側片之前端部(3a)側之端部或其附近的前端側接著劑層(36)，且側片(3)包含將配置於內表面側之片材(31)與肌膚側片材(21)接合的上側接合部(66)，上側接合部(66)與本體側接著劑層(35)於尿布厚度方向上重疊。
