PURPOSE: To enable the discrimination of wire gages numbers of wires by reproducing code numbers corresponding to wire gages detecting induced magnetic fields with a signal detecting section as generated by a tone burst signal when tone burst signals representing code numbers corresponding to wire gages of wires are applied to the wires in a time division manner.

CONSTITUTION: As a circular arc-shaped magnetic core bar coil 31 of a wire signal detecting section 5 is brought close to any one of wires being exposed, the coil 31 thereof 5 picks up induced magnetic fields formed by a tone burst signal current flowing through the wires and a tone burst signal current representing code numbers of (m) bits corresponding to wire gages is inputted into a tone burst demodulation section 34 as induced in the coil 31. Thus, serial data of code numbers corresponding to the wire gages are outputted from the tone burst demodulation section 34, converted into a parallel data with a serial-parallel conversion section 35 and indicated on a display 36 to discriminate wire gages. Tone bursting signals T1...Tn representing code numbers of (m) bits corresponding to respective wire numbers No.1...n are applied to the wires continuously and repeatedly in time division fashion.