PURPOSE: To obtain a stable braking force by applying a braking force between a disc formed of a material having a hysteresis coefficient secured to one of rotor side or stator side and the magnetic flux of a permanent magnet provided on the opposite side in the manner of facing the disc via air-gap by means of the both disc and flux.

CONSTITUTION: A permanent magnet 8 secured integrally with a yoke 7 made of magnetic material to the rear of the stator 1 of a motor with the magnetized surface of the magnet directed to the direction opposite to that of the stator 1. On the other hand, a boss 4 with a disc 3 formed of a material having a suitable hysteresis coefficient secured thereto is attached to a rotor shaft projecting from the rear of the stator 1 so that the disc 3 faces the permanent magnet 8 via air-gap 6. The magnetic flux of the permanent magnet 8 returns between the disc 3 and yoke 7 facing through the air-gap 6, and when the motor rotates, a magnetic pole acts on the disc 3 while a change is delayed by hysteresis characteristics and a braking force is applied to a rotor 2. This brake requires no power and has no friction member so that its braking force is constant without changing.