PURPOSE: To increase the ventilating efficiency in an engine room of an automobile by utilizing both the inside of a side frame of an engine room side and the inside of an underframe located under floor as a ventilating passage for an engine room.

CONSTITUTION: Side frame 1 in an engine room and an underframe 6 located under a floor panel 4 are formed into a closed section, while the fore portion of the underframe 6 and the hind portion of the side frame 1 are connected through. In the inside surface of the side frame 1, holes 12 which connect the inside of the side frame 1 with the engine room 8 are made. And in the bottom surface of the underframe 6, holes 13 which connect the inside of the frame 6 to the outside of an automobile are made. Since hot air in the engine room enters the frame 6 through the holes 12 and is discharged through the holes 13, the ventilation of the engine room can be carried out effectively.