In an arc detector, a frequency analyzer analyzes frequency components of a current subject to detection in a first frequency band. A detector detects an occurrence of an arc by referring to the frequency components in the first frequency band. When the detector does not detect the occurrence of an arc by referring to the frequency components in the first frequency band, the frequency analyzer analyzes frequency components of the current subject to detection in a second frequency band lower than the first frequency band, and the detector detects the occurrence of an arc by referring to the frequency components in the second frequency band.