A simple structure capable of preventing a cam part of an actuator from coming out of position when the actuator is in an open position. The cam part 12a of the actuator 12 for rotating contacts 13 mounted inside an insulating housing 11 is provided with an engaging surface 12a2 which is a flat surface that faces cam lock protrusions 13a2 of second contact beams 13a when the actuator 12 is in the open position. Upon an external force or the like acting on the cam part 12a to come out of cam rotation recesses 13b3 when the actuator 12 is in the open position, the engaging surface 12a2 of the cam part 12a abuts on and makes locking engagement with the cam lock protrusions 13a2, so that the actuator 12 is prevented from coming out of position.