We have developed a new protocol for measuring direct current (DC) resistivity data, in which self-potential (SP) data were measured immediately prior to obtaining the resistivity data. Based on this SP measurement, we have defined two different resistances: the forward resistance (i.e., a normalized potential difference caused by forward current injection) and the backward resistance (i.e., a normalized potential difference caused by backward current injection). This has allowed us to quantify distortions in the DC resistivity potential field caused by all unknown mechanisms, including ambient noises. In accordance with the proposed measurement protocol, we further devised a data-weighting method in a resistivity inversion for calculating more reasonable subsurface structures, and the method was based on the forward and backward resistances. Through inversion experiments using field resistivity data acquired by the proposed protocol, we have determined the validity and effectiveness of the proposed method.