In a reflow soldering apparatus comprising a conveyor 4 to transport circuit boards 5 mounted with electronic components into multiple chambers 1, 2 and 3, and fans 6 installed in the chambers 1, 2 and 3, the centers of the impellers in the adjacent fans 6 are not on a single perpendicular plane along the transport line of the conveyor and arrayed offset to the left and right. This apparatus may also employ a structure wherein the centers of the impellers in the adjacent fans are not on a single horizontal plane and arrayed offset up and down. Further, it may also employ a structure wherein the fans are arranged with their rotation shafts inclined.