PURPOSE: To facilitate an investigation of ground water, investigation of a landslide, etc., by supplying the current to be supplied to the ground as DC or alternating DC of a long period and making survey from the change quantity in the specific resistance value of the ground and the potential difference between potential electrodes.

CONSTITUTION: The potential difference generated in the ground by the current of the constant voltage DC or constant DC supplied to the ground by the current electrodes 8, 9 is detected by potential electrodes 10, 11 and the potential difference generated by the current passed to the ground is detected and amplified via an S.P. compensating unit 12 which erases the natural potential of the ground. The amplified potential difference and current are recorded as the change quantity of the potential difference and the change quantity of the current in a recorder 16. The resistance value obtd. by computing the voltage/current by an arithmetic unit 15 is recorded to a recorder 16 simultaneously therewith. Recording as an analog waveform to the recorder 16 is possible in this case or displaying and recording by digitizing the characteristics of the analog waveform are also possible. The alternating DC can be generated by operating a current rectifier unit 17 in the case of supplying the alternating DC of the long period.