A small country congested with roads and buildings such as Japan, magnetic noise is comparatively great and in many cases it exceeds the magnetic anomalies to be detected. A pair of proton magnetometers connected electrically to work as a sort of differential-type magnetometer satisfied basic requirements. Results of basic experiments applied to a kiln site and a dwelling site are given, and a method to visualize the data by means of a Sony Tektronix 4051 graph-generator was described. -- AATA