Attaching structure capable of preventing a service-plug from exposure to water

An attaching structure for attaching a service-plug (4) for shutting off and conducting an electric circuit of a vehicle to a power source device (1) , comprises a floor metal plate (2) constituting a bottom wall of a compartment of the vehicle and formed with an opening (21) which faces the compartment; a metal plate (3) disposed outside the vehicle under the floor panel and forming a cavity (S) between the metal plate (3) and the floor metal plate (2) and covering the power source device (1) , and including an attachment portion (31) to which the service-plug (4) is attached and raised toward the opening in the cavity (S); and a sealing member (5) for keeping the cavity liquid-tight disposed between the floor metal plate (2) and the metal plate (3) so as to surround the attachment portion; the service-plug (4) is detachably attached to the attachment portion so as to project toward the compartment through the opening.