A reverse input shutoff clutch , comprising: an input member ; an output member coaxially arranged with the input member ; a pressed member having a pressed surface ; and an engaging element that, when a rotational torque is inputted to the input member , moves in a direction away from the pressed surface due to engagement with the input member , and by engaging with the output member , transmits the rotational torque that is inputted to the input member to the output member ; and when a rotational torque is reversely inputted to the output member , moves in a direction toward the pressed surface due to engagement with the output member , and by coming in contact with the pressed surface , completely shuts off not to transmit the rotational torque that is reversely inputted to the output member , or transmits part of the rotational torque that is reversely inputted to the output member to the input member , and shuts off a remaining part of the rotational torque that is reversely inputted to the output member , wherein the pressed surface is an arc-shaped concave surface, and pressing surfaces that are pressed against the pressed surface are provided at two positions spaced apart in a circumferential direction of the engaging element , the pressing surfaces respectively being constructed by a cylindrical convex surface having a radius of curvature that is smaller than the radius of curvature of the pressed surface , characterized in that a cross-sectional shape of the pressed surface and a cross-sectional shape of the pressing surfaces of the engaging element pressed against the pressed surface are both arc shaped, and a radius of curvature of the cross-sectional shape of the pressing surfaces is made smaller than a radius of curvature of the cross-sectional shape of the pressed surface . an input member ; an output member coaxially arranged with the input member ; a pressed member having a pressed surface ; and an engaging element that, when a rotational torque is inputted to the input member , moves in a direction away from the pressed surface due to engagement with the input member , and by engaging with the output member , transmits the rotational torque that is inputted to the input member to the output member ; and when a rotational torque is reversely inputted to the output member , moves in a direction toward the pressed surface due to engagement with the output member , and by coming in contact with the pressed surface , completely shuts off not to transmit the rotational torque that is reversely inputted to the output member , or transmits part of the rotational torque that is reversely inputted to the output member to the input member , and shuts off a remaining part of the rotational torque that is reversely inputted to the output member , wherein the pressed surface is an arc-shaped concave surface, and pressing surfaces that are pressed against the pressed surface are provided at two positions spaced apart in a circumferential direction of the engaging element , the pressing surfaces respectively being constructed by a cylindrical convex surface having a radius of curvature that is smaller than the radius of curvature of the pressed surface , characterized in that a cross-sectional shape of the pressed surface and a cross-sectional shape of the pressing surfaces of the engaging element pressed against the pressed surface are both arc shaped, and a radius of curvature of the cross-sectional shape of the pressing surfaces is made smaller than a radius of curvature of the cross-sectional shape of the pressed surface . <EOS>