To quickly, easily and precisely measure the azimuth and inclination of a stratum by arranging gravity sensors in two axes and geomagnetic sensor in three axes, and arithmetically processing their output electric signals.

Since the partial force of gravity in one axis can be calculated by measuring the magnitudes of partial forces in the other two axes, sensors can be reduced for two axes by omitting the sensor for one axis. The electric signals measured by five sensors in total of gravity sensors 2 and geomagnetic sensors 3 are amplified, converted into digital signals Mx, My, Mz, Gx, Gy by an A/D converter 5, and then inputted to an arithmetic device 6. The device 6 calculates the geomagnetic azimuth θi and inclination i formed with horizontal plane by operation based on the signals Mx, My, Mz, Gx, Gy, and outputs them to a memory device 8. The output control to a display device 9 and the data transfer control to an external input and output device 10 are performed by a control device 7. The number of the sensors 2 is reduced to two, by which a small-sized device can be economically constituted, and the azimuth θi and the inclination i can be automatically measured at the same time.