PURPOSE: To provide an inter-electrode/base material distance measuring method with high speed and high accuracy in the short-circuit shifting area of a low current.

CONSTITUTION: Short-circuited time in the short-circuit shifting area of the low current is measured in short-circuited time measuring processing 4. Also, a short-circuited time rate within measuring time is calculated from the short- circuited time measured in the short-circuited time measuring processing 4. A reference short-circuit current and a reference arc current are referred from a short-circuit/arc current parameter table 8 in reference current decision processing 9, and a reference current is decided based on the short-circuited time rate. Distance between a welding electrode and the base material is calculated by comparing a measured mean current with a decided reference current in inter-electrode/base material distance calculation processing 10.