PURPOSE: To make it possible to apply a magnetic field with higher magnetic flux density to an inspection object with a broad width along with stabilization of a detection sensitivity, by arranging a number of E-shaped cores wound with electromagnetic coils on the one side of the inspection object in order to generate a magnetic field.

CONSTITUTION: A magnetic field generating device 13 constituted by E-shaped cores 15 wound with electromagnetic coils 14 permits the magnetic field to be applied to an inspection object 12 and detects a change of magnetic flux density of the magnetic field caused by existence of metal in said object to detect metal. The magnetic field generating device 13 with a space part 18 is arranged in large numbers in the width direction of the inspection object 12, and when a switch 25 of a central controlling device 24 turns on, the electromagnetic coils 14 are supplied with current by an AC power source 19, thereby allowing a magnetic field to be applied to the inspection object 12 through bakelite 16. Therefore, when the inspection object 12 is made to travel on a guide member 22 as shown by arrows 23, magnetic flux density changes if a piece of metal 26 is intermixed. This change is further detected by a detector 20, amplified and indicated by a metal detection indicator 21.