When an operation body is urged upward by a flat spring and is in a return position, a projection disposed on the operation body is held between opposing positioning portions and the position of the operation body in an X-direction is set. When the operation body is pressed at a position away from a central portion of the operation body in the X-direction, the operation body pivots on one of retaining structures downward. At this time, the projection moves away from the opposing positioning portions, and resistance against a pressing operation can thereby be reduced.