An underpants-type disposable diaper comprising: an integral outer body extending over a front body and a back body or an outer body separately provided to the front body and the back body; an inner body attached to an intermediate portion of the outer body in a width direction, the inner body extending over the front body and the back body; side seal portions obtained by bonding both side portions of the outer body in the front body and both side portions of the outer body in the back body, respectively; a waist opening and a pair of right and left leg openings; an absorber provided in a range including a back end portion of the inner body; and a stretchable region contracting in the width direction on a waist side of a back end portion of the absorber in the back body, the underpants-type disposable diaper further comprising a barrier sheet that extends from a position on a front side of a back end of the absorber to a back side thereof and extends outward in the width direction from positions of both side edges of the absorber in the width direction, wherein the barrier sheet has a free part not bonded to a member on a back surface side and a fixed part bonded to the back body, the free part is located at least in a middle of a part overlapping the absorber in the width direction in the barrier sheet and is continuous from a front edge to within a range of ±10 mm before and after a back edge of the absorber in the barrier sheet, the dimension of the free part in the width direction is 70 to 90% of the dimension of the inner body in the width direction, the fixed part surrounds a back side and both sides in the width direction of the free part, and a width direction inner edge of a part of the fixed part located on both sides of the free part in the width direction is on an outer side of a side edge of the inner body in the width direction and adjacent to the side edge of the inner body or is located on the inner body, a pocket-shaped dorsal side barrier having an inlet opening to a crotch side is formed by the free part of the barrier sheet, the outer body does not have the stretchable region in an overlapping part between the free part of the barrier sheet and the absorber, a torsion hardness of a predetermined part including the back end portion of the absorber is 0.18 to 0.32 N·cm/cm, where the torsion hardness means a value measured by a test Torsion hardness as described in the description and in the predetermined part including the back end portion of the absorber, a total basis weight of pulp fibers and super absorbent polymer particles is 350 to 600 g/m2, a weight ratio of the super absorbent polymer particles to the pulp fibers is 40 to 60%, and a thickness is 6 to 12 mm. an integral outer body extending over a front body and a back body or an outer body separately provided to the front body and the back body; an inner body attached to an intermediate portion of the outer body in a width direction, the inner body extending over the front body and the back body; side seal portions obtained by bonding both side portions of the outer body in the front body and both side portions of the outer body in the back body, respectively; a waist opening and a pair of right and left leg openings; an absorber provided in a range including a back end portion of the inner body; and a stretchable region contracting in the width direction on a waist side of a back end portion of the absorber in the back body, the underpants-type disposable diaper further comprising a barrier sheet that extends from a position on a front side of a back end of the absorber to a back side thereof and extends outward in the width direction from positions of both side edges of the absorber in the width direction, wherein the barrier sheet has a free part not bonded to a member on a back surface side and a fixed part bonded to the back body, the free part is located at least in a middle of a part overlapping the absorber in the width direction in the barrier sheet and is continuous from a front edge to within a range of ±10 mm before and after a back edge of the absorber in the barrier sheet, the dimension of the free part in the width direction is 70 to 90% of the dimension of the inner body in the width direction, the fixed part surrounds a back side and both sides in the width direction of the free part, and a width direction inner edge of a part of the fixed part located on both sides of the free part in the width direction is on an outer side of a side edge of the inner body in the width direction and adjacent to the side edge of the inner body or is located on the inner body, a pocket-shaped dorsal side barrier having an inlet opening to a crotch side is formed by the free part of the barrier sheet, the outer body does not have the stretchable region in an overlapping part between the free part of the barrier sheet and the absorber, a torsion hardness of a predetermined part including the back end portion of the absorber is 0.18 to 0.32 N·cm/cm, where the torsion hardness means a value measured by a test Torsion hardness as described in the description and in the predetermined part including the back end portion of the absorber, a total basis weight of pulp fibers and super absorbent polymer particles is 350 to 600 g/m2, a weight ratio of the super absorbent polymer particles to the pulp fibers is 40 to 60%, and a thickness is 6 to 12 mm.