To provide a technique capable of accurately deciding normal/defective condition of resistance welding during or immediately after the implementation without being least affected by external disturbance or the like.

The resistance welding machine comprises: a first welding electrode; a second welding electrode; an energizing means for making a welding current flow between the first and second welding electrodes through a workpiece; a ultrasonic transmitter installed on the first welding electrode side; a ultrasonic receiver installed on the second welding electrode side; and an inter-electrode timer that measures time from the point of time at which the ultrasonic transmitter transmits a ultrasonic wave until the point of time at which the ultrasonic receiver receives it.