A two-way clutch has a rotational driving unit, a rotational driven unit, a roller interposed between the rotational driven unit and a collar, which is a fixed member and is not rotatable. A recess is formed in an inner peripheral surface of the collar, so that the roller is engaged with the recess. As a result, a locked condition between the rotational driven unit and the collar by means of the roller is not easily released. Therefore, the rotational driven unit is stably held at its locked position, even when a high vibration, a high load and/or a large pulsation is applied to the rotational driven unit.