PURPOSE: To equalize the distribution of temperature in a car room without decreasing the passenger room space in a car, by both providing evaporator units at positions diagonally in front and rear car walls and mounting cooling air ducts in an opposite direction on the ceiling and side walls.

CONSTITUTION: A plurality of evaporator units 3, 3' are provided in such a manner that the both units 3, 3' are at a position diagonally to each other with one of them in the front end wall of a car 1 and the other of them in the rear end wall. Then cooling air ducts 15, 15' for distributing cooling air supplied from the units 3, 3' into a car room 17 are mounted to both corner parts in which a ceiling crosses with side walls and formed in a reverse direction to each other in such a manner that the cooling air is blown from the front to rear by the cooling air duct 15 connected to the unit 3 in the front end wall of the car and from the rear to front by the cooling air duct 15' connected to the unit 3' in the rear end wall of the car. In this way, temperature in the car room 17 can be equally distributed further with no specific necessity for enlarging the passenger room space.