PURPOSE: To detect abnormality of rotary moving body due to sticking, for example.

CONSTITUTION: In a device comprising a magnetic moving body contained movably in the axial direction in a rotating housing 11 and a solenoid 17 disposed on the outside of the housing 11 such that the moving body is located substantially in the center wherein the moving body is moved axially by the electromagnetic force of the solenoid 17, transient response of current flowing through the solenoid 17 is monitored upon turn OFF thereof and a decision is made whether the current has a magnitude lower than a predetermined value during a time interval after elapse of a first predetermined time before elapse of a second predetermined time. A decision is made that the moving body is abnormal if the magnitude of the current is not lower than the predetermined value.