A method and device for producing a minus-ion air similar to a heated compressed hot air stream, electromagnetic waves in the far-infrared and submilimeter region (hereinafter referred to as ''terahertz wave'') by regulating the discharge pressure and the discharge temperature. The device is excellent in versatility, small in size, and low in cost. An object processed by using the method and device, a processing method, and a processing apparatus are also provided. Air is sent from a blower or an air compressor (2) through an air pipe (8) to a heated compressed air regulator (vessel (3)). The air sealed in the heated compressed airregulator (1) regulated under a predetermined discharge pressure (for example, 30 kPa to 150 kPa) and at a temperature (40 DEG C to 250 DEG C) is passed through a through hole (4A) of a circular plate (4) to produce a heated compressed air. In the produced hot air stream, a resonance electromagnetic wave resonating with the natural frequency of the water molecule is generated by a terahertz wave and a generated thermal shock wave, thereby the hydrogen bond of the water molecules in the air is cut, and electrons are released from hydrogen atoms, thus also producing a minus-ion air stream. A processed object, a processing method, and a processing apparatus are so constituted that the produced hot air stream is used for drying, production of a functional water by exposing water to the hot air stream, production of an aqueous fuel, beauty/health appliances, air/water quality improvement devices, combustion efficiency enhancement devices for internal combustion engines, and so forth.