The present invention provides an apparatus and method enabling to perform a 2-dimensional trajectory analysis applicable for a three-phase system. A signal analysis apparatus generates a three-row and N-column waveform matrix constituted by three N dimensional row vectors having respectively N samples of first to third phase current values obtained from three-phase current signals measured in a three-phase system, where N is the number of samples of each of the three-phase current signals in one cycle of an AC power supply; applies transformation to the waveform matrix to obtain a two-row and N-column matrix constituted by the first and second N dimensional row vectors; performs normalization in amplitude of the first and second N dimensional row vectors, respectively; selects a grid size based on the sample number N; and maps a two dimensional trajectory made up from the first and second normalized N dimensional row vectors on a grid with the grid size selected.