1. An image analysis method comprising: acquiring an image of an observation region including a plurality of pixels respectively having a plurality of time-serially acquired data; setting an analysis region on the image of the observation region; setting a sub-analysis region smaller than the analysis region; intermittently moving the sub-analysis region in increments of a pixel interval over the entire analysis region; executing correlation analysis using data of pixels in the sub-analysis region every time the sub-analysis region is moved, so as to estimate at least a molecular number or a diffusion constant of the sub-analysis region; and forming a molecular number or diffusion constant image by mapping the molecular numbers or the diffusion constants.