To improve a seating property of a mounting member with respect to a supporting member and enhance the positional accuracy of the mounting member. The mounting member has a protruding portion that protrudes from a support face of a frame body, and a shaft body that is thinner than the protruding portion. At a base portion of the shaft body, a relief recess is formed over the entire circumference of a boundary region with the protruding portion, and a supported face of the protruding portion is configured so as to contact with a support face of the frame body in a state in which the mounting member is supported by the frame body. In a preferred embodiment of the present invention, the mounting member is used as a guide pin of a floating plate that accommodates an IC socket.