PURPOSE: To stop an operating rotating equipment at an arbitrarily set reference position.

CONSTITUTION: The number of rotation (n) of a rotating equipment 1 is measured by a rotary encoder 3 disposed at an air spindle 2. When the number of rotation (n) is less than the arbitrarily set reference value, and a notch K1 disposed on the work of the rotating equipment is detected by a photosensor F, a switching valve V is operated, and a cylinder S disposed at a position opposed to the notch K2 is driven, so that a rod R can be operated, inserted into a notch K2, and the work can be stopped.