To provide a device in which an upper heated air is also used for blowing off from the bottom and capable of blowing off at the same tempera ture and wind velocity in a lead-free reflow furnace in which substrates and electronic components or the like are necessary to be heated by the hot air whose temperature and wind velocity being the same as those at its middle and four corners.

The hot air which has been heated at the part upper than the conveying substrate is used together with the blown-off hot air from the lower part via a passageway. The hot air is blown against the substrate via a tank in which a plate for buffering the hot air shock is used so that the upper and lower hot air pressure are blown against the substrate at the same temperature and wind velocity. Thereby, the air of the same temperature and wind velocity is blown against the middle and the four corners, etc., of the substrate.