An underpants-type disposable diaper, in which a front side outer member disposed in a front body and a back side outer member disposed in a back body are separately provided, each having an inner surface and a back surface, the front side outer member and the back side outer member are spaced apart in the front-back direction _at the middle in the front-back direction, an inner member having a liquid pervious top sheet, a liquid impervious sheet, and an absorber interposed therebetween extends in the front-back direction from the front side outer member to the back side outer member, the inner member is joined to each of the front side outer member and the back side outer member on their inner surfaces, a cover nonwoven fabric covering a back surface of the inner member is provided from between the front side outer member and the inner member to between the back side outer member and the inner member, both sides of the front side outer member and both sides of the back side outer member are joined to each other to form said inner and outer surfaces, a waist opening and a pair of right and left leg openings are included, and elastic members are incorporated in the front side outer member and the back side outer member, wherein the cover nonwoven fabric is provided with a plurality of holes penetrating a front surface and a back surface of the cover nonwoven fabric from between the front side outer member and the inner member to between the back side outer member and the inner member at intervals, and the front side outer member and the back side outer member have, at least at portions overlapping with the cover nonwoven fabric and not having any elastic member, a total luminous transmittance of 50% or more measured according to JIS-K 7105, characterized in that at least either of the front side outer member and the back side outer member is joined to the inner member, at regions overlapping with both end portions in the width direction of the inner member, and is not joined or is intermittently and peelably joined to the inner member, at a part on a crotch side or a whole part in the front-back direction of a region between the regions overlapping with the both end portions in the width direction of the inner member. an inner member having a liquid pervious top sheet, a liquid impervious sheet, and an absorber interposed therebetween extends in the front-back direction from the front side outer member to the back side outer member, the inner member is joined to each of the front side outer member and the back side outer member on their inner surfaces, a cover nonwoven fabric covering a back surface of the inner member is provided from between the front side outer member and the inner member to between the back side outer member and the inner member, both sides of the front side outer member and both sides of the back side outer member are joined to each other to form said inner and outer surfaces, a waist opening and a pair of right and left leg openings are included, and elastic members are incorporated in the front side outer member and the back side outer member, wherein the cover nonwoven fabric is provided with a plurality of holes penetrating a front surface and a back surface of the cover nonwoven fabric from between the front side outer member and the inner member to between the back side outer member and the inner member at intervals, and the front side outer member and the back side outer member have, at least at portions overlapping with the cover nonwoven fabric and not having any elastic member, a total luminous transmittance of 50% or more measured according to JIS-K 7105, characterized in that at least either of the front side outer member and the back side outer member is joined to the inner member, at regions overlapping with both end portions in the width direction of the inner member, and is not joined or is intermittently and peelably joined to the inner member, at a part on a crotch side or a whole part in the front-back direction of a region between the regions overlapping with the both end portions in the width direction of the inner member.