PURPOSE: To provide a reliable, durable mechanism for restricting the rotational direction of a small motor.

CONSTITUTION: When a permanent magnet rotor 11 rotates in the forward direction, a magnet attraction member 19 moves forward by the attraction of the permanent magnet. This motion of the member 19 actuates a link 30 to take the end 25 of a lever 23 out of the circular path of an engaging piece 18 of the rotor 11, so that the rotor continues the forward rotation. When the rotor 11 rotates in the reverse direction, on the other hand, the attraction member 19 moves backward by the attraction of the permanent magnet. This motion of the member 19 actuates the link 30 to bring the end 25 of the lever 23 into the circular path of the projection 18 of the rotor 11. Therefore, the projection 18 abuts on the end 25 to prohibits reverse rotation of the rotor.