A constant velocity universal joint, comprising: an outer joint member (55, 62); an inner joint member; and a torque transmission member which is interposed between the outer joint member (55, 62) and the inner joint member, the outer joint member (55, 62) having an opening portion sealed with a boot (80A, 80B), the boot (80A, 80B) comprising: a large-diameter mounting portion which is mounted to a boot receiving portion (85, 86) formed on a radially outer surface of the outer joint member (55, 62) on an opening portion side; a small-diameter mounting portion which is mounted to a boot receiving portion (85, 86) on a shaft fitted to the inner joint member; and a bent portion which connects the large-diameter mounting portion and the small-diameter mounting portion to each other, the large-diameter mounting portion being fastened and fixed by a fastening clamp (82A, 82B) in a state of being externally fitted onto the boot receiving portion of the outer joint member (55, 62), the small-diameter mounting portion being fastened and fixed by a fastening clamp (83A, 83B) in a state of being externally fitted onto a boot receiving portion of the shaft, the large-diameter mounting portion comprising: a circumferential clamp groove to which the fastening clamp (82A, 82B) is fitted, the circumferential clamp groove being formed in an outer peripheral surface of the large-diameter mounting portion; and a protruding portion formed on a boot (80A, 80B) outer side end portion of the inner peripheral surface of the large-diameter mounting portion, the boot receiving portion (85, 86) being a cylindrical surface of the outer joint member (55, 62) comprising: a recessed portion to which the protruding portion of the large-diameter mounting portion is fitted; and a projection formed in a vicinity of a boot (80A, 80B) inner side of the recessed portion, characterized in that: the boot receiving portion (85, 86) and the inner peripheral surface of the mounting portion of the boot (80A, 80B) facing the boot receiving portion (85, 86) on a joint opening side of the projection are brought into close contact with each other in a fastened state by the fastening clamp (82A, 82B, 83A, 83B). an outer joint member (55, 62); an inner joint member; and a torque transmission member which is interposed between the outer joint member (55, 62) and the inner joint member, the outer joint member (55, 62) having an opening portion sealed with a boot (80A, 80B), the boot (80A, 80B) comprising: a large-diameter mounting portion which is mounted to a boot receiving portion (85, 86) formed on a radially outer surface of the outer joint member (55, 62) on an opening portion side; a small-diameter mounting portion which is mounted to a boot receiving portion (85, 86) on a shaft fitted to the inner joint member; and a bent portion which connects the large-diameter mounting portion and the small-diameter mounting portion to each other, a large-diameter mounting portion which is mounted to a boot receiving portion (85, 86) formed on a radially outer surface of the outer joint member (55, 62) on an opening portion side; a small-diameter mounting portion which is mounted to a boot receiving portion (85, 86) on a shaft fitted to the inner joint member; and a bent portion which connects the large-diameter mounting portion and the small-diameter mounting portion to each other, the large-diameter mounting portion being fastened and fixed by a fastening clamp (82A, 82B) in a state of being externally fitted onto the boot receiving portion of the outer joint member (55, 62), the small-diameter mounting portion being fastened and fixed by a fastening clamp (83A, 83B) in a state of being externally fitted onto a boot receiving portion of the shaft, the large-diameter mounting portion comprising: a circumferential clamp groove to which the fastening clamp (82A, 82B) is fitted, the circumferential clamp groove being formed in an outer peripheral surface of the large-diameter mounting portion; and a protruding portion formed on a boot (80A, 80B) outer side end portion of the inner peripheral surface of the large-diameter mounting portion, a circumferential clamp groove to which the fastening clamp (82A, 82B) is fitted, the circumferential clamp groove being formed in an outer peripheral surface of the large-diameter mounting portion; and a protruding portion formed on a boot (80A, 80B) outer side end portion of the inner peripheral surface of the large-diameter mounting portion, the boot receiving portion (85, 86) being a cylindrical surface of the outer joint member (55, 62) comprising: a recessed portion to which the protruding portion of the large-diameter mounting portion is fitted; and a projection formed in a vicinity of a boot (80A, 80B) inner side of the recessed portion, a recessed portion to which the protruding portion of the large-diameter mounting portion is fitted; and a projection formed in a vicinity of a boot (80A, 80B) inner side of the recessed portion,