In a predetermined first state, a distance (D1) in a second direction between a contact portion (Pin) between a input-side engaging part (9) and an input-side engaging part (17) and a rotation center (O) is larger than a distance (D2) in the second direction between a contact portion (Pout) between an output-side engaging part (12) and an output-side engaged part (14) and the rotation center (O). In a locked state or a semi-locked state, a contact portion (C1) between the output-side engaging part (12) and the output-side engaged part (14) is located closer to the rotation center (O) of the output member (4) in a first direction than an imaginary straight line (L) connecting a contact portion (C2) between one pressing surface (13) of the pair of pressing surfaces (13) and a pressed surface (6) to the rotation center (O) of the output member (4).