A woman's undergarment comprising: a pair of left and right brassiere cups each configured to receive a breast and having a lower edge, a side edge, and an upper edge, the lower edge being downwardly curved, the side edge rising from an underarm-side end of the lower edge toward the upper edge, the upper edge extending from a sternum-side end of the lower edge to an upper end of the side edge; cup cover pieces each disposed to cover an outer surface of the brassiere cup and separated from the outer surface of the brassiere cup; a back piece extending from lateral sides of the cup cover pieces and configured to cover a wearer's back; and straps each extending from the cup cover piece to the back piece, wherein: only the lower edge of the brassiere cup extending from the underarm-side end to the sternum-side end is sewn to a lower edge of the cup cover piece, and the side edge and the upper edge of the brassiere cup are free edges detached from the cup cover piece, characterized in that: the woman's undergarment further comprises a cup connecting piece for connecting abutting portions of the left and right brassiere cups, each of the cup cover pieces includes: a cover piece body that covers the outer surface of the brassiere cup; and an upper edge reinforcing strip sewn to an upper edge of the cover piece body, and a lower end portion of one of the upper edge reinforcing strips and a lower end portion of another of the upper edge reinforcing strips overlap each other to form a double-layer region, and the overlapping lower end portions (29c, 29d) are sewn together to a lower edge of the cup connecting piece. a pair of left and right brassiere cups each configured to receive a breast and having a lower edge, a side edge, and an upper edge, the lower edge being downwardly curved, the side edge rising from an underarm-side end of the lower edge toward the upper edge, the upper edge extending from a sternum-side end of the lower edge to an upper end of the side edge; cup cover pieces each disposed to cover an outer surface of the brassiere cup and separated from the outer surface of the brassiere cup; a back piece extending from lateral sides of the cup cover pieces and configured to cover a wearer's back; and straps each extending from the cup cover piece to the back piece, wherein: only the lower edge of the brassiere cup extending from the underarm-side end to the sternum-side end is sewn to a lower edge of the cup cover piece, and the side edge and the upper edge of the brassiere cup are free edges detached from the cup cover piece, characterized in that: the woman's undergarment further comprises a cup connecting piece for connecting abutting portions of the left and right brassiere cups, each of the cup cover pieces includes: a cover piece body that covers the outer surface of the brassiere cup; and an upper edge reinforcing strip sewn to an upper edge of the cover piece body, and a lower end portion of one of the upper edge reinforcing strips and a lower end portion of another of the upper edge reinforcing strips overlap each other to form a double-layer region, and the overlapping lower end portions (29c, 29d) are sewn together to a lower edge of the cup connecting piece. the woman's undergarment further comprises a cup connecting piece for connecting abutting portions of the left and right brassiere cups, each of the cup cover pieces includes: a cover piece body that covers the outer surface of the brassiere cup; and an upper edge reinforcing strip sewn to an upper edge of the cover piece body, and a lower end portion of one of the upper edge reinforcing strips and a lower end portion of another of the upper edge reinforcing strips overlap each other to form a double-layer region, and the overlapping lower end portions (29c, 29d) are sewn together to a lower edge of the cup connecting piece.