Metal detector

A metal detector comprising:

• a magnetic field output unit configured to generate an alternating magnetic field in a transport path of an inspection object;
• a magnetic field detection unit configured to detect a change in magnetic field caused by the inspection object passing through the alternating magnetic field to output a detection signal;
• a metal determination unit configured to determine whether or not metal is contained in the inspection object based on the detection signal;
• a storage unit configured to sequentially store, as influence value information, information including phase information and amplitude information that is obtained based on the detection signal when an accepted product passes through the alternating magnetic field, the accepted product being the inspection object that is determined not to contain metal by the metal determination unit;
• a state change determination unit configured to determine whether or not a state of the inspection object is changed based on whether or not the influence value information exceeds a predetermined criterion;
• and
• a notification unit configured to notify, when the state change determination unit determines that the state of the inspection object is changed, the determination.