To simplify positioning of each contact plate so that the positioning thereof may be correspondent to various switches by sufficiently enlarging the opening part of a case of switch in comparison with the flat surface parts of a movable contact plate and a fixed contact plate.

A fixed contact plate 6 is positioned by means of a projection 1a in the inside of a case 1. A movable contact plate 4 is positioned by the side surface of the fixed part position 4c of a movable contact plate 4 and the inner wall of the case 1 and fixed by caulking a dowel 1b. Since the case 1 has a wide open end, a total error in assembly work becomes small. A movable contact 3 is spring energized by the elasticity of the movable contact plate 4 to fixed contact 5 attached to the fixed contact plate 6. When electric current flows from a lead terminal 7 to the fixed contact plate 6 and an electric current larger than that in a normal case owing to lock, etc., of the motor flows, the movable contact plate 4 generates heat to deform a snap mechanism part 4b. Owing to this event, the movable contact 3 comes in its non-engaged state electrically with the fixed contact 5 so as to cut electric current.