An apparatus for measuring the specific resistivity of rock samples over the range 106-10-3 Omega m is described. The meter consists of three different sample holders and an electronic central unit. The sample holders can be applied to drill core (diameter 30 mm) and block samples. Specific resistivities can be determined in different directions. The measurement is based on the four-point method using a 1 kHz AC source. The instrument is easy to use and provides results quickly. Samples with rough surfaces can also be measured. The specimen can be rotated and moved during the measurement so that the effects of inhomogeneity and anisotropy can be observed. The instrument has been used successfully in prospecting.