NOVELTY - The attachment body (2) has multiple batteries (30) fixed in a battery assembly (3). An electrical wire leading-out part (10) is connected to an electrical wire accommodating part (9) that accommodates multiple electrical wires (5) connected with corresponding terminals (4) in the battery assembly. A cover (11) is fixed to the electrical wire accommodating part by sliding inside an opening part of the electrical wire accommodating part along a direction from an end (3b) to another end (3a) of the battery assembly so as to cover the opening part.    USE - Battery assembly attachment body for a power supply device of a hybrid vehicle and an electric vehicle.    ADVANTAGE - The cover is fixed to the electrical wire accommodating part by sliding inside the opening part of the electrical wire accommodating part so as to cover the opening part, thus preventing the electrical wire from being damaged during assembly of the batteries. The design of the attachment body eliminates the need for a locking mechanism such as a lock receiving part and a lock claw part, thus reducing size of the attachment body, and hence saving installation space of the attachment body. The electrical wire accommodating part can be provided with inner walls and a holding part for holding the cover, so as to prevent deformation of the cover for improving the attachment property of the cover, and to prevent distribution of the electrical wires at two sides of the inner wall and twisting of the electrical wires. The attachment body can be provided with a pair of ribs vertically arranged at the ends of the cover, so as to increase strength of an edge part of the cover.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a power supply device comprising a battery assembly attachment body. '(Drawing includes non-English language text)'    Battery assembly attachment body (2)    Battery assembly (3)    Ends of battery assembly (3a, 3b)    Terminals (4)    Electrical wires (5)    Electrical wire accommodating part (9)    Electrical wire leading-out part (10)    Cover (11)    Batteries (30)