PROBLEM TO BE SOLVED: To provide a method and an apparatus for the detection of magnetism, in which the magnetism is hardly affected by the shape and the characteristic of a core and in which the magnetism can be measured by using an AC exciting signal at a high frequency.
SOLUTION: In a sensor head 1, a coil 4 for excitation is wound on the upper part of a core 2 composed of a high-permeability magnetic material, and a coil 6 for detection is wound on the lower part of the core 2. An AC signal source 20 and a DC signal source 24 are connected respectively to the coil 4 for excitation via a resistance 22 and a resistance 26. A DC signal by the DC signal source 24 is applied to an AC exciting signal by the AC signal source 20, and the coil 4 for excitation is excited. The DC signal by the DC signal source 24 shifts the AC exciting signal, in such a way that magnetism in the entire positive region or the entire negative resion of the AC exciting signal becomes the magnetically saturated region of the core 2. An amplifier 30 which amplifies a detection signal, a synchronous detection signal 32 and a low-pass filter 34 are connected to the coil 6 for detection.