Abstract: A memory (33) is provided for storing in advance data of signals supplied from a detector unit (26) when a plurality of metallic foreign matter samples differing in magnitude passes an alternating field, and data representing the magnitude of each foreign matter sample. A setting device (32) causes an indicator 36 to display the magnitude of metal detectable by a determination device (31) on the basis of those data on the foreign matter samples. Further, a contained metal displaying device (34), when the determination device (31) has determined that metallic foreign matter is contained in the object of inspection, displays the magnitude of that metal content on the indicator (36). The user can intuitively grasp the detectable magnitude of metal and the magnitude of the metal contained in the object of inspection.