To enable both advantages of hot air drying and dehumidifying drying to be provided and concurrently their disadvantages to be accommodated from each other, improve a drying efficiency and quality and at the same time minimize a running cost.

A blower 30 is directly driven by an engine 20 and air heated to cause its temperature to be increased by radiation heat of the engine 20 is supplied by the blower 30 to a storing tank. A part of the heated air of which temperature is increased is sent to the blower 30 through a dehumidifier 40. A power generator 60 is driven by the engine 20.