A casing comprises substantially symmetrical first and second divided casings. A second blower unit is provided at a joined region of the first divided casing and the second divided casing. Air is supplied from a first blower unit into the casing, and then, the air cooled by an evaporator and the air heated by a heater core are mixed and supplied to front seats in the vehicle. Air supplied from the second blower unit into the casing is directed toward the front seats and adjusted at a given temperature by a second cooling section of the evaporator and a second heating section of the heater core, and thereafter, supplied to rear seats in the vehicle from a third rear passage which extends so as to surround a first rear passage.