Patent ID: 7193413

Claim:
A magnetic field measurement apparatus comprising: a first magnetometer having a pick-up coil for picking up a magnetic field generated from an examination object; a first control unit for controlling the first magnetometer; a second magnetometer for picking up an interference magnetic field; a second control unit for controlling the second magnetometer; a modulation circuit for modulating an output from the second control unit; a current converter for converting the output from the modulation circuit to a current amount; a current amount adjusting means for adjusting the current amount thus converted; a coil which is positioned outside the pick-up coil of the first magnetometer and through which the current thus adjusted by the current amount adjusting means flows; a demodulation circuit which demodulates the output from the first control unit with the same frequency as that of the modulation circuit; a low-pass filter for extracting a low frequency element of the output voltage from the demodulation circuit; and a subtraction circuit for subtracting an output of the low-pass filter from the output of the first control unit.