PURPOSE: To enable the discrimination of wire gages of wires by counting the number of induced magnetic fields as signal corresponding to wire gages detecting them with a signal detection section as generated by a tone burst signal current when tone burst signals are applied in the number corresponding to the wire gages of wires composing a wire cable.

CONSTITUTION: As a circular arc-shaped core bar coil 31 of a wire signal detecting section 5 is brought close to any one of wires exposed, the coil 31 of thereof 5 picks up induced magnetic fields formed by a tone burst signal current of wires and a tone burst signal current induced in the coil 31 is inputted into a demodulation circuit 34 continuing in the number corresponding to the wire gate. Clock signals continuing in the number corresponding to each of the wire gages (for example, continued three clock signals if the wire gage of a wire being inspected is No.3) is outputted intermittently and counted up with a counter section 35. The counts thereof express the wire numbers and are indicated on a display 36 to determine the wire gages. If any disconnection exists, no signal current flows when the wire signal detecting section 5 is brought close to the wire disconnected. The dislay 36 indicates no wire gage number thereby enabling the discrimination of disconnection.