PURPOSE: To increase the withstand voltage between contacts in a balanced armature type by providing a simultaneously off type contact structure such that when a magnetic pole portion at one end of an iron core attracts one end of a contact, both of the movable contacts of a contact spring separate from fixed contacts.

CONSTITUTION: A contact spring 5 comprises leg pieces 51, 52 and a center piece 50 having a step and has movable contacts 5a, 5b secured to its ends, and a contact spring 6 is constructed likewise. A hinge spring piece 4 secured to the springs 5, 6 and to an armature 3 is formed integrally with an insulator 7 at the center of the armature 3. The armature 3 is rocked about a rib provided at its center, and the springs 5, 6 are moved correspondingly so that pairs of fixed contacts 1a, 1b and 1c, 1d of a base 1 alternately make and break; i.e., a simultaneously off type and 1a1b type contact structure is provided, in which the interval between the contacts is twice the distance between the movable and fixed contacts, resulting in an increase in withstand voltage. Center pieces 50, 60 inside the insulator 7 are curved at more than a predetermined distance from the armature 3 so as to be surely insulated.