PURPOSE: To prevent an effect on a heat-sensitive element for an overload protective device of heat generated from an element for a starter by installing first and second partition walls between the starter and the overload protective device and forming an air layer between the partition walls.

CONSTITUTION: Recessed sections in which a starter 22 and an overload protective device 23 are housed are shaped to an approximately square-shaped case 21. A first partition wall 24a partitioning the starter 22 and the overload protective device 23 and a second partition wall 24b extended up to the position of approximately three quarters from the sidewall of the case are mounted, and a third partition wall 24c vertically dividing the first partition wall 24a and the second partition wall 24b is set up. Air layers 25c, 25d are formed among each partition wall. Accordingly, an adverse effect on the overload protective device 23 of heat generated from an element for the starter section 22 can be prevented.