PURPOSE: To simplify a construction, make a car body light, and effectively use a space by installing an air introducing path and an air discharge path in a battery compartment, and positioning an inlet of the air introducing path in the positive pressure part of a car and an outlet of the discharge path in the negative pressure part.

CONSTITUTION: An air introducing path D is formed in the front of a battery compartment C and an air discharge path H is in the rear. The introducing path D is formed in such a way that a wind introducing plate 35 is mounted in the back of air passing hole 34 which is installed in a floor panel 21 to form air flow path between the wind introducing path D and the panel 21, and an air introducing hole 36 is positioned in the positive pressure part which is generated by air flowing along a car body during car traveling. The air discharge path H is formed in such a way that an air flow path is formed by air passing holes 37 and 38 which are installed in a rear separating plate 24 and an inner panel 32a of a back door 32 respectively and an outer panel 32b of the back door 32, and an air discarge hole 39 is positioned in the negative pressure part which is generated by air flowing along the car body.