PROBLEM TO BE SOLVED: To establish compatibility between easiness of loading and unloading of the penis and prevention of leakage from a penis insertion part.SOLUTION: In an underpants-type disposable diaper, a penis insertion part 30 communicating with the inside and the outside is provided on the waist side of an absorber 13 of an exterior body 20, and a folding expansion/contraction part 40 for increasing/decreasing a vertical length on the waist side with respect to the penis insertion part 30 is provided.