The present invention provides an apparatus and a method for operating reflow soldering in a mounting field whereby an abnormality in transfer of circuit boards can be detected with high reliability. Whether or not a circuit board is transferred by a transfer conveyor is judged. A discharge conveyor is started when a control device judges occurrence of transfer abnormality. After the discharge conveyor starts, the transfer abnormality is determined to be a drop of the circuit board if a discharge completion detector detects that a dropped circuit board is discharged. And then the control device continues the reflow soldering. The transfer abnormality in the reflow soldering apparatus can be detected with high reliability because it can be detected whether the transfer abnormality is either the drop or a clog of the circuit board.