NOVELTY - The structure has air intake duct (12) that is extended towards battery unit (11). The cooling air is supplied to unit by using air of compartment (5). An air-intake grill is attached to rear portion of vehicle (10). An air-intake side opening portion (13) of duct is covered by forming several air-intake holes. The coiling air is intake into duct by cooling fan (14). The air-intake grill forms main inlet port (20), while opening area of auxiliary air intake (30) is smaller than grill formed in alignment portion of window (16) that is arranged in rear portion.    USE - Cooling structure of battery unit in vehicle such as hybrid vehicle and electrical vehicle.    ADVANTAGE - The air of compartment is taken as cooling air for emergency, and supplied to battery unit, so that the battery cooling capability is securable and the abnormal temperature raise of battery unit is prevented. The deterioration of the battery characteristics is prevented and the durability of the battery is improved. The air intake duct that supply requisite air quantity can be positioned in cooling battery unit of small vehicle in restrained space. The small vehicle with few installation spaces can provide main inlet port where opening area is large. The auxiliary air intake provides a good-looking inlet port, without increasing the number of portions due to gap formed in the alignment portion of an interior element and a window. The cost of the air intake is reduced. The appearance of the auxiliary air intake is excellent without using exclusive components, so that the cost of the air intake is reduced. The cooling air of the compartment taken from auxiliary air intake and battery are cooled effectively. Since the connection with the auxiliary air intake and the opening portion of duct are blocked, the suction noise from the air intake in usual time is prevented. Thus the passengers are comfort in traveling in vehicle. The air intake for emergency is arrange in the structure, so that the cooling air required for cooling battery is securable even in emergency with which the main inlet port is taken.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic side view of the hybrid vehicle.    Compartment (5)    Vehicle (10)    Battery unit (11)    Air intake duct (12)    Air-intake side opening portion (13)    Cooling fan (14)    Window (16)    Main inlet port (20)    Auxiliary air intake (30)