PURPOSE: To remove a loss due to a pattern of a printed circuit board by eliminating the need for due consideration to be taken into of a current capacity in a primary winding of a current transformer concerning an eddy current detector in which a wire led out of an electric part is coupled direct to a pattern of the printed circuit board through a core of the current transformer.

CONSTITUTION: An eddy current detector has a current transformer 2 carried on a printed circuit board 6 to detect a current flowing through an electric part 1 and a wire 10 led out of the electric part 1. One of the wire 10 is put through a core 21 of the current transformer 2 directly and then the end of the wire 10 is coupled to a pattern 7 of the printed circuit board 6.