A method for significantly reducing measurement time for electrical resistivity profiling and logging without degrading the quality of the measurement includes simultaneously transmitting a current from multiple points to underground and carrying out mathematic processing to calculate a potential obtained when a current is transmitted independently from any transmission point, based on observed response potential waveforms. Further current waveforms having a covariance of zero are selected. Then, a possible response obtained independently at transmission point can be determined by dividing the covariance of the observed potential waveform and the current waveform by the variance of the current waveform. As the waveform zeroing the covariance, an M-sequence code with zero added to the end thereof is applied.