In an automotive air conditioner, there is provided an air guide arrangement for achieving an effective mixing between cooled air from an evaporator and warmed air from a heater under a bi-level mode. The air guide arrangement is placed in the vicinity of an outlet opening of a warmed air passage extending from the heater. The air guide arrangement forces a warmed air from the outlet opening of the warmed air passage to effectively mix with a cooled air which flows in a direction from the evaporator toward a ventilation air outlet opening.