PURPOSE: To prevent damage to a fitting device equipped with two or more chucks by allowing the chuck in service to retract when a set of parts can not be fitted together with the aid of an autormatic abnomality sensing system.

CONSTITUTION: If, in a device where parts 33 held by two or more floating heads 14 are one after another fitted on or in other parts, any pair of of the parts can not be fitted the floating head 14 holding said pair is acted by a force upward or sidewise to distort a ring-shaped rubber member 21, and either the cylinder 23, is pushed up or set in eccentricity from the vertical position. A limit switch 9 senses this rise or eccentricity with the aid of a moved lever 10 to send an electric signal to the auromatic control device 52. Now a solenoid operated valve 51 is actuated to contract the cylinder 2 and to operate an alarm device 53.