PURPOSE: To maintain the effect of a contact spring almost equal to that when a fixed contact is in a closed state, even with opening movement of the fixed contact, to obtain a big opening distance by setting the angle of inclination of a long hole such that a pin located at the lower end portion of the long hole starts to slide toward the upper end portion of the long hole when the fixed contact is rotated to some extent from its closed state against the contact spring.

CONSTITUTION: When a fixed contact 3 is rotated the angle of inclination of a long hole 18 is increased as compared to when the contact is in its closed state. Frictional forces between a pin 17 and the inner peripheral face of the long hole 18 are therefore decreased and, when the fixed contact 3 is rotated to some extent the pin 17 starts to slide toward the upper end portion of the long hole 18. The pin 17 locates at the upper end portion of the long hole 18 at that moment when the fixed contact 3 finishes its opening movement. The spring force of a contact spring 15 which temporarily increases is maintained at that condition when the pin 17 starts its sliding movement, and will not increase any more. Even when the opening distance of a movable contact 4 is increased, the spring force of the contact spring is therefore maintained at a value approximating that obtained when the contact is in its closed state.