The present invention is equipped with: mounting cables; jumper cables (23); connection-receiving plugs attached to the ends of the mounting cables; connecting plugs attached to the ends of the jumper cables (23); a housing (10) that is installed beneath the floor of the vehicle, and on the inter-vehicle-side face of which is formed an aperture part into which the connecting plugs are guided, with the connection-receiving plugs being guided in from the face on the opposite side of the inter-vehicle-side face and connecting to the connecting plugs; a water-blocking frame (2) that is attached in a removable manner to the inter-vehicle-side face of the housing (10), and on which a slanting face is formed having inlet holes with which the connecting plugs are guided in obliquely from below the inter-vehicle-side face; and fastening parts (5) that are attached to the slanting face (2b), fastening in place the jumper cables (23).