PURPOSE: To detect large current in the state being insulated from a current supplying conductor by equidistantly disposing four or more gaps on the circumference of a ring form iron core.

CONSTITUTION: A ring form iron core 2 penetrated by a current supplying conductor 3 is disposed. In case a magnetic flux passed the face of Hall elements 1, the voltages corresponding to the number of magnetic fluxes are generated at voltage terminals V1, V2 due to the relation of currents and magnetic fluxes. On the other hand, there are parallel connection and series connection as the construction of obtaining the mean value voltage of the output voltages of the Hall elements 1. The Hall elements 1 generate voltages according to magnetic fields, but the Hall elements per se have internal resistances and therefore in the case of the parallel connection, the mean value of the output voltages of the entire Hall elements generate in the output terminals.