A module is configured to be attached to a cage. A handle is rotatable about a rotation shaft between an accommodated position where the module is mounted to the cage and a withdrawal position where the module can be withdrawn from the cage. A resiliently-bendable tongue piece performs engagement and disengagement between the module and the cage. A notch portion is provided to the tongue piece. A press portion is provided to the handle on a circumference having a center located on the rotation shaft of the handle, the press portion configured to contact with the notch portion when the handle is at the accommodated position. A cam rotatable with the handle so as to resiliently bend the tongue piece.