To prevent generation of frost at a lower coolant passage member or the like and fluctuation of blowing temperature of cooled air from an evaporator by promoting evaporation of the liquid coolant apt to stay in a lower part of the evaporator, in particular, in the lower coolant passage member.

The air cooling unit (cooling device) used in an air conditioner for a vehicle is provided with a cylindrical duct 10 for forming a passage of air; a flat core 32 stored in the duct; and the evaporator 30 including the tubular lower coolant passage member 36 mounted to a lower end of at least the core. The duct 10 is provided with an air introduction passage 20 for leading the air before passing through the core to the lower coolant passage member and a lower end 33a of the core. Since the air of relatively high temperature before passing through the core is led to the lower coolant passage member and its periphery, evaporation of the coolant in the lower coolant passage member is promoted.