To provide an air chiller device for an aircraft with an improved drain valve for dew condensation.

The air chiller device comprises the drain valve 160 mounted in a drain port of a drain pan and consisting of a valve seat member 162 having an opening portion 162a at the center and a valve member 164 put and mounted on the lower face of the valve seat member 162. The valve member 164 is formed of a thin silicone rubber and a valve element 164e is supported by an extremely small spring constant by a slit formed arm 164b. During the operation of the air chiller device, the valve element 164e is put in close contact with the opening portion 162a of the valve seat to close the drain valve. When the operation is stopped and water droplets are put on the valve element 164e, the valve element 164e is flexed to open it with the weight thereof. With no water droplets, it closes the same to prevent the entry of moisture.