PURPOSE: To enable unloading operation to be sufficiently followed up by connecting a quick discharging circuit in parallel to a capacitor for taking out operating current of an electronic timer element.

CONSTITUTION: A fourth resistor 14 connected in series to a constant voltage diode 11 is connected in parallel to a second capacitor 15. An integrating circuit is constituted from these fourth resistor 14 and second capacitor 15. Both terminals 15a, 15b of the second capacitor 15 are connected to a second terminal 13a of a trigger terminal and a fifth terminal 13b of a control terminal of a timer element 13 so that unloading opration of sufficient follow-up can be carried out even for a short time between stoppage and restart of an electric motor for driving a compressor body.