Provided is a technique for improving connection reliability. A contact part that contacts with a detecting male contact is formed in a detecting collision spring piece. The detecting male contact includes a contact surface that contacts with the contact part. The detecting collision spring piece is elastically deformed in advance so that a gap is formed between the contact part and the contact surface when the contact part is opposed to the contact surface in a height direction. When an elastic deformation force that elastically deforms the detecting collision spring piece is released, the contact part contacts with the contact surface with collision against the contact surface due to a spring restoring force of the detecting collision spring piece. A locus of the contact part just before the contact part collides with the contact surface is oblique with respect to the contact surface when seen from a mate direction.