A clutch comprising: an inputting member rotatable by input of an input torque; a rotatable outputting member to which the input torque is transmitted through said inputting member; a stationary member including a cylindrical inner wall surface surrounding said inputting member and said outputting member and configured to be mounted on a mounting portion in a rotation-prevented state; and a contact member contactable to said inputting member, said outputting member and said stationary member, wherein said outputting member includes an output contact portion (2a, 2b) contactable to an input engaging portion of said inputting member, wherein said contact member is positioned between said outputting member and said stationary member and includes an arcuate first contact surface contacting the cylindrical inner wall surface of said stationary member and a second contact surface contactable to said output contact portion (2a, 2b), and wherein when the input torque for rotating said inputting member in one rotational direction is inputted, said outputting member and said contact member rotate in contact with said inputting member, characterized in that when a reverse input torque for rotating said outputting member in said one rotational direction is inputted, the input engaging portion of the inputting member and the output contact portion (2a, 2b) of the outputting member are spaced from each other, and said output contact portion (2a, 2b) of said outputting member urges the first contact surface against the cylindrical inner wall surface of said stationary member by urging the second contact surface of said contact member thereby to prevent rotation of said outputting member. an inputting member rotatable by input of an input torque; a rotatable outputting member to which the input torque is transmitted through said inputting member; a stationary member including a cylindrical inner wall surface surrounding said inputting member and said outputting member and configured to be mounted on a mounting portion in a rotation-prevented state; and a contact member contactable to said inputting member, said outputting member and said stationary member, wherein said outputting member includes an output contact portion (2a, 2b) contactable to an input engaging portion of said inputting member, wherein said contact member is positioned between said outputting member and said stationary member and includes an arcuate first contact surface contacting the cylindrical inner wall surface of said stationary member and a second contact surface contactable to said output contact portion (2a, 2b), and wherein when the input torque for rotating said inputting member in one rotational direction is inputted, said outputting member and said contact member rotate in contact with said inputting member, characterized in that when a reverse input torque for rotating said outputting member in said one rotational direction is inputted, the input engaging portion of the inputting member and the output contact portion (2a, 2b) of the outputting member are spaced from each other, and said output contact portion (2a, 2b) of said outputting member urges the first contact surface against the cylindrical inner wall surface of said stationary member by urging the second contact surface of said contact member thereby to prevent rotation of said outputting member.