PURPOSE: To miniaturize a device and improve the signal-to-noise ratio by impressing pulsed direct current signals to a source axis to reduce field distortion, and using a remote sensor responding to the change rate of the electromagnetic field.

CONSTITUTION: A device 10 is composed of a source 12 of the electromagnetic field, a remote sensor 14 and an electrode unit 16. The source 12 supplies each pulsed direct current signal time-division-multiplexed, to antennas 18, 20, 22 from current drivers 24, 26, 28 and generates the mutually identifiable electromagnetic field. In this case, a processor 36 impresses the pulse signals repeatedly for time enough to reduce field distortion caused by an eddy current generated to conductive metal existing in the surroundings. The antennas 44, 46, 48 of a sensor 14 respond to the change rate dB/dt of the electromagnetic field, integlate (60, 62, 64) amplified voltage and output them to terminals 66, 68, 70. A multiplexer 72 connects these output to an analog-to-digital converter 76 in regular order to send them to a CPU 36 so as to compute the position and azimuth of the sensor 14 in the reference coordinate frame of the source 12.