To provide simple construction for energy efficient and stable supply of dry air to a dryer even at a low temperature without the need for a defroster or reverse operation of refrigerant by utilizing exhaust heat from the dryer even at a low temperature when defrost is formed on an evaporator.

This air supply device 1 comprises a condenser 2 and the evaporator 3. The inside of the device 1 is divided into a condenser chamber 7, an evaporator chamber 8 and a flow path change-over chamber 9, and air is supplied from the evaporator chamber 8 to the flow path change-over chamber 9. The flow path change-over chamber 9 has switches 11, 12 attached to an opening communicated with the outside and an opening communicated with the condenser chamber 7, respectively, for changing over a flow path. The air is supplied from the condenser chamber 7 to the dryer 20. An exhaust pipe 23 from the dryer 20 is connected to a selector valve 15 which selects the air to be introduced as exhaust air from the dryer or atmospheric air to the evaporator 3.