NOVELTY - The structure (48) has a battery unit (20) with an operating portion (40) e.g. power supply circuit interrupting device, which protrudes toward a service hole (16) formed in a vehicle floor. A service hole cover (50) includes a housing recessed portion (56) that is arranged in the service hole, where the service hole cover covers the operating portion. The cover has a bent-back portion (52) that is bent back toward outer side of the housing recessed portion and toward vehicle floor side from a lower end portion (60L) of the recessed portion.    USE - Service hole cover mounting structure for use in a battery mounting structure (claimed) of a vehicle e.g. electric vehicle, petrol hybrid vehicle and fuel cell hybrid vehicle.    ADVANTAGE - The battery unit supports an extended portion through a seal when the cover is attached to the floor, such that horizontal displacement of an extended part with respect to the battery unit is inhibited, thus easily deforming the bent-back portion towards a housing recessed portion side with the extended portion as a fulcrum when the bent-back portion is pressed toward the operating portion of the battery unit by the vehicle floor, and hence inhibiting contact between the housing recessed portion and the operating portion of the battery unit when collision occurs. The seal is provided between the extended portion and the battery unit, such that rainwater and dust are inhibited from entering the housing recessed portion, thus improving the durability of the battery unit. An electrical circuit of a battery module is able to be electrically interrupted by removing the service hole cover from the vehicle floor and operating an operating part of the operating portion of the battery unit through the service hole during maintenance of the battery unit, thus improving maintenance on the battery unit.    DESCRIPTION OF DRAWING(S) - The drawing shows an enlarged sectional view of a service hole cover.    Service hole (16)    Battery unit (20)    Operating portion (40)    Service hole cover mounting structure (48)    Service hole cover (50)    Bent-back portion (52)    Housing recessed portion (56)    Lower end portion of housing recessed portion (60L)