To improve the positioning accuracy and operation reliability of a switching mechanism which performs positioning by being energized to one direction and to allow smooth coordinated operation to be carried out even when the mechanism is built into a limited space.

When an operating member 15 exists in a second operative position, a cam part 75a of a projection 75 for beam attenuation disposed integrally with the operating member 15 and a touch part 77a of a lift piece 77 of a beam attenuating lever 68 touch each other at a small pressure angle. When the operating member 15 is turned to a third operative position, the touch state is switched during the course thereof and the touch part 75b touches the cam part 77b at the small pressure angle α. The pressure angle α can be suppressed to specified magnitude or below and the smooth cooperation can be carried out even in the limited space or under conditions of a fulcrum and working point. When the operating member 15 arrives at the third operative position, an arcuate surface 75c made into the circle concentric with the turning center of the operating member 15 receives the lift piece 77 and therefore the position of the lever 68 is stabilized.