A two-stage thermostatically operated switching mechanism has two toggle switches supported on different levels of an insulator support. The switches have a common terminal member for fixed contacts and movable contacts of the respective switches are operated by overcenter spring mechanisms actuated by a common lever connected with an expansible power element. The overcenter operating mechanism of one switch has an elongated tension spring which is connected with a movable control arm and is caused to shift from one side to the other of dead center by the common lever. The pivot for the contact arm is shiftable towards and from the actuating lever by a screw adjustment.