In control motors having an armature rotatable counter to a spiral spring, a problem arises that the set force of the spiral spring can be changed by the process of installation. The disclosed control motor is intended to enable setting of the force of the spiral spring after installation. To enable setting of the force of the spiral spring after installation, relative to which an armature of a control motor is rotatable, a shaft on which the armature is supported is screwed with a screw end into a threaded bore of a housing bottom end. Connected to the shaft is an adjusting element, which with a driver arm engages an end portion provided on the outer end of the spiral spring. By rotating the ends of the shaft, which are accessible from outside, the force of the spiral spring can be changed. The invention is preferably applicable to idling adjusters, but it is not limited to this field of application.