Abstract: Provided is a metal detector capable of quickly and accurately ascertaining a noise generating situation. A metal detector generates a magnetic field in an inspection region and detects a change in the magnetic field in the inspection region to detect a foreign substance in an inspection object passing through the inspection region. The metal detector measures the change in the magnetic field of the inspection region while changing an inspection frequency, performs frequency analysis of the measurement result, and displays an obtained frequency distribution diagram on the display unit as a noise diagnosis result. In the frequency distribution diagram, target foreign substance reference lines are displayed.