Gaps that divide a conductive portion include an I-shaped gap that passes through the center of a fixed contact, and L-shaped gaps that are located on both sides of the I-shaped gap. Longitudinal gap of the L-shaped gaps extend beyond a virtual straight line A-A that passes through the center of the fixed contact and extend in the direction orthogonal to the I-shaped gap, and are connected to lateral gaps. The L-shaped gaps are arranged point-symmetrically about the center of the fixed contact.