A disposable undergarment comprising: a ventral member and a dorsal member that are bonded to each other at both bonded portions (5a, 5b) along both end portions in a waist-around direction; a crotch member that is bonded to and bridges between both center portions (2c, 3c) of the ventral member and the dorsal member; a waist opening defined by both upper edges (7, 8) of the ventral member and the dorsal member; left and right leg openings (9a, 9b) defined by the ventral member, the dorsal member, and the crotch member; and a first elastic member that extends upward toward the upper edges from lower portions of the bonded portions (5a, 5b) of the ventral member to a center in the waist-around direction, wherein the ventral member has a lower edge including: both end lines (10a, 10a) substantially in parallel with the waist-around direction; a pair of inclined lines (10b, 10b) extending upward toward a side of the upper edge, from the both end lines (10a, 10a) toward the center portion; and a center line connecting between the inclined lines (10b, 10b); wherein the dorsal member has a lower edge including: both end lines (11a,11a) substantially in parallel with the waist-around direction; a pair of inclined lines (11b,11b) extending downward toward a side opposite to the upper edge, from the both end lines (11a,11a) toward the center portion; and a center line connecting between the inclined lines (11b,11b), wherein a hip-surrounding elastic member (12a to 12c) extending in the waist-around direction in the ventral member has higher tensile force than a hip-surrounding elastic member (12d to 12f) extending in the waist-around direction in the dorsal member; wherein the disposable undergarment has a shape widening from the waist opening toward the left and the right leg openings (9a, 9b) on a lower side, and wherein the upper edge of the ventral member has a center portion disposed lower than the upper edge of the dorsal member. a ventral member and a dorsal member that are bonded to each other at both bonded portions (5a, 5b) along both end portions in a waist-around direction; a crotch member that is bonded to and bridges between both center portions (2c, 3c) of the ventral member and the dorsal member; a waist opening defined by both upper edges (7, 8) of the ventral member and the dorsal member; left and right leg openings (9a, 9b) defined by the ventral member, the dorsal member, and the crotch member; and a first elastic member that extends upward toward the upper edges from lower portions of the bonded portions (5a, 5b) of the ventral member to a center in the waist-around direction, wherein the ventral member has a lower edge including: both end lines (10a, 10a) substantially in parallel with the waist-around direction; a pair of inclined lines (10b, 10b) extending upward toward a side of the upper edge, from the both end lines (10a, 10a) toward the center portion; and a center line connecting between the inclined lines (10b, 10b); both end lines (10a, 10a) substantially in parallel with the waist-around direction; a pair of inclined lines (10b, 10b) extending upward toward a side of the upper edge, from the both end lines (10a, 10a) toward the center portion; and a center line connecting between the inclined lines (10b, 10b); wherein the dorsal member has a lower edge including: both end lines (11a,11a) substantially in parallel with the waist-around direction; a pair of inclined lines (11b,11b) extending downward toward a side opposite to the upper edge, from the both end lines (11a,11a) toward the center portion; and a center line connecting between the inclined lines (11b,11b), both end lines (11a,11a) substantially in parallel with the waist-around direction; a pair of inclined lines (11b,11b) extending downward toward a side opposite to the upper edge, from the both end lines (11a,11a) toward the center portion; and a center line connecting between the inclined lines (11b,11b), wherein a hip-surrounding elastic member (12a to 12c) extending in the waist-around direction in the ventral member has higher tensile force than a hip-surrounding elastic member (12d to 12f) extending in the waist-around direction in the dorsal member; wherein the disposable undergarment has a shape widening from the waist opening toward the left and the right leg openings (9a, 9b) on a lower side, and wherein the upper edge of the ventral member has a center portion disposed lower than the upper edge of the dorsal member.