To provide a reversing inhibition device capable of preventing the generation of breakdown even if the excessive rotary driving force due to the working force from a load side is generated.

A ratchet gear of a ratchet mechanism for checking the rotation of a screw member is formed freely to be turned without integrally fixing it with a screw member, and when the action force is applied to this screw member from a load side, the magnetic force by an electromagnet is generated by existence of this action force so as to conclude the checking. When a rotary driving shaft 5 is driven for rotation in the case of operation for device, a ball screw rod 6 is rotated so as to move a ball and nut rod, namely, an output shaft forward, but since a load exists, and the force of the load is detected by a detecting part 30 through a pressure receiver board 21F. Consequently, electric energy is applied to a magnetized coil 23 through an amplifier 31 in the case of operation for drive, and the electromagnet is operated so that the magnetic force (attracting force) works between a permanent magnet 22. With this structure, checking force is applied to the rotation by a function of a ratchet mechanism.