A welding power supply including an inverter circuit that converts DC power to high frequency AC power, a welding transformer that performs voltage adjustment on the high frequency AC power, a DC converting means (24,25) including a DC reactor that generates DC output voltage suitable for welding from a secondary side AC power of the welding transformer, an arc producing means for producing an arc to weld a welding subject by supplying the generated output power to an electrode, a detecting means (33,34) for detecting an output current and an output voltage when the output power is generated, and a controlling means for calculating a voltage at a tip of the electrode based on the detected output current and output voltage and controlling the inverter circuit based on the calculated tip voltage, the welding power supply being characterized in that: the DC reactor includes a first characteristic, in which an inductance is constant in a high current range, and a second characteristic, in which the inductance increase as the current decreases in a low current range; a resistance calculating means for calculating a total resistance in a path from the welding power supply to the electrode tip based on the output voltage when the inverter circuit controls the output current at a predetermined current in a state in which the electrode and the welding subject is short circuited; an inductance calculating means for detecting at least three inductances based on a current attenuation amount related to at least one value of the output current corresponding to a range of the first characteristic and a current attenuation amount related to at least two values of the output current corresponding to a range of the second characteristic of the DC reactor in a state in which the electrode and the welding subject is short circuited, and calculating a total inductance in the path from the welding power supply to the electrode tip from a function of at least three previously detected inductances; and the first characteristic is a normal characteristic and the second characteristic is an oversaturated characteristic; a tip voltage calculating means for calculating the tip voltage of the electrode; wherein the tip voltage calculating means is configured so that the number of detections of the inductance for the range of the second characteristic is more than the number of detections of the inductance for the range of the first characteristic; and a tip voltage correcting means for correcting the tip voltage in accordance with a voltage change related to the total resistance and the total inductance in the path from the welding power supply and the electrode tip for the detected output voltage; the DC reactor includes a first characteristic, in which an inductance is constant in a high current range, and a second characteristic, in which the inductance increase as the current decreases in a low current range; a resistance calculating means for calculating a total resistance in a path from the welding power supply to the electrode tip based on the output voltage when the inverter circuit controls the output current at a predetermined current in a state in which the electrode and the welding subject is short circuited; an inductance calculating means for detecting at least three inductances based on a current attenuation amount related to at least one value of the output current corresponding to a range of the first characteristic and a current attenuation amount related to at least two values of the output current corresponding to a range of the second characteristic of the DC reactor in a state in which the electrode and the welding subject is short circuited, and calculating a total inductance in the path from the welding power supply to the electrode tip from a function of at least three previously detected inductances; and the first characteristic is a normal characteristic and the second characteristic is an oversaturated characteristic; a tip voltage calculating means for calculating the tip voltage of the electrode; wherein the tip voltage calculating means is configured so that the number of detections of the inductance for the range of the second characteristic is more than the number of detections of the inductance for the range of the first characteristic; and a tip voltage correcting means for correcting the tip voltage in accordance with a voltage change related to the total resistance and the total inductance in the path from the welding power supply and the electrode tip for the detected output voltage;