An aspect of the present disclosure calculates a phase variance value indicating a degree of variance of a phase in a surrounding of each position in a biological tissue, based on phase values of excitation wave at respective positions in the biological tissue that acts in response to excitation caused by propagation of the excitation wave in the tissue, and generates an analysis map, based on a time series of at least part of the phase variance values at the respective positions. Since the phase variance value indicates the degree of variance of the phase in the surrounding, a position having a large degree of variance of the phase in the surrounding may be specified as a rotation center of rotating excitation wave.