An analysis method is provided that ensures objective and quantitative analysis for analyzing time-series images. For implementing the method are provided an image data storage unit that stores therein image data on a plurality of time-series computed tomography (CT) images of an organ of a subject captured after a contrast medium has been administered; a target pixel extraction unit configured to extract an intra-organ pixel position, which is a position of a pixel in a region of the organ; a change-over-time determining unit configured to determine a change-over-time of a CT value of the pixel at the determined intra-organ pixel position, based on image data on the time series CT images in the plurality of frames; and a function approximation processing unit configured to determine an arrival time at which the contrast medium has arrived at an organ at the intra-organ pixel position and a base value, which is a CT value serving as a base of the pixel at the intra-organ pixel position, based on the determined change-over-time.