A high-performance drilling bit for geothermal well drilling is expected to be developed to reduce the drilling duration and cost. The application of polycrystalline diamond compact (PDC) bits to geothermal well drilling has been considered worldwide. In this study, drilling tests on several types of rock were performed in a laboratory using a PDC bit. The drilling parameters changed reasonably in the tests according to the rock properties. The progress of the wear of PDC cutters was quantitatively observed and was found to be associated with some of the indexes of rock abrasivity.