An underpants-type disposable diaper includes outer members 12F and 12B having stretchable regions A2 and A3 disposed adjacent to the inner edges of the side seal portions 12A in the width direction. The stretchable regions A2 and A3 include multiple elongated elastically stretchable members 19 disposed between two sheet layers 12S and 12H at predetermined intervals in the front-back direction and extending in the width direction. The elastically stretchable members 19 each include two fixed ends 19f fixed to the two sheet layers 12S and 12H, and the section between the fixed ends 19f is unfixed to the two sheet layers 12S and 12H. The two sheet layers 12S and 12H are welded into sheet bonding sections 20, at positions between the elastically stretchable members 19 in the stretchable regions A2 and A3 adjacent in the front-back direction. No sheet bonding section protrudes from the side seal portion in the stretchable regions A2 and A3.
