PURPOSE: To stop a rotary body and prevent overrunning thereof by arranging a drum with a positioning hole and a pin fitted into the hole elastically sliding on the drum in a positioning apparatus for the rotary body.

CONSTITUTION: Holes a1, a2 and b1, b2 are provided separately on the circumference of drums 2 and 3 mounted on a rotary shaft 1 at intervals of 180°. The hole of one drum is arranged to be shifted by 90° from the hole of the other drum. With the changeover of a solenoid valve 14, air is fed to a cylinder 13 while upon the release of air in a cylinder 12 by a spring 16, the pin 10 brakes to prevent overrunning of the rotating shaft elastically contacting the shaft. As the shaft turns by 90°, the pin 10 fits into the hole 11 to forcibly stop the rotation thereof thereby assuring an angle of rotation of 90° exactly.