A plurality of projection images are obtained, on a basis of plural pieces of three-dimensional image data obtained by imaging an object at a plurality of different time points, by projection from a plurality of different projection directions corresponding to projection images in accordance with a three-dimensional partial region where a pixel value is increased and a three-dimensional partial region where the pixel value is decreased at a second time point with respect to a first time point among the plurality of time points, and the plurality of projection images are displayed on a display unit.