PROBLEM TO BE SOLVED: To provide an underpants type disposable diaper having side seal parts hardly stimulating the skin of a wearer.SOLUTION: An underpants type disposable diaper 1 includes a crotch part C, a ventral part A and a dorsal part B, and a pair of side seal parts S. In a state before the diaper 1 is worn, each side seal part S extends linearly along a longitudinal direction X of the diaper compared with a worn state of the diaper 1. In the worn state, the side seal part extends in a meandering manner along the longitudinal direction X of the diaper 1. The side seal part S includes a connection part extending along the longitudinal direction X of he diaper 1. It is preferable that a non-connection part is not present outward the connection part in the lateral direction Y of the diaper 1.
