To stop a table under a fixed state even if power supply is interrupted by an arrangement wherein a retainer is urged oppositely to the moving direction through a linear solenoid.

An urging means, i.e., a coil spring 8, has one end engaged with the stop plate 15 of an outer cylinder 6 while being enclosed thereby, and the other end for urging a retainer 4 oppositely to the moving direction through a solenoid 7 by pressing the end part thereof. When the solenoid 7 is conducted, a plunger 7a is pulled in against the the coil spring 8 and a ball 5 is separated from the tapered face 6a of the outer cylinder 6 in the direction shown by an arrow P. The ball 5 rolls freely as a shaft member 2 moves so that the shaft member 2 can move freely. When power supply to the solenoid 7 is interrupted, the retainer 4 is urged to move by the coil spring 8 and the ball 5 is stopped on the tapered face 6a of the outer tube 6 through wedge action of the shaft member 2. According to the structure, a table is stopped under fixed state when power supply is interrupted.