The welding device of the present disclosure has a switching section, a setting section, an output detector, a controller, a frequency controller, and a driver. The switching section is formed of a switching element. The setting section determines setting output. The output detector detects welding output. The controller calculates an output-on period of the switching section according to the setting output and the welding output. The frequency controller determines an inverter frequency based on the output-on period. The driver controls on/off operation of a switching element of the switching section based on the inverter frequency and the output-on period. When the output-on period is calculated using a first ratio, the inverter frequency is determined to a first frequency, and when the output-on period is calculated using a second ratio smaller than the first ratio, the inverter frequency is determined to a second frequency higher than the first frequency.