1. A fluorescent signal analyzing apparatus comprising: an image input unit to which at least one fluorescent image of a sample is input; a storage unit to store data on the at least one fluorescent image input to the image input unit; an extracting unit to extract, for each of the fluorescent images, data on a fluorescence intensity in a desired region on the at least one fluorescent image from the data on the at least one fluorescent image stored in the storage unit; and an analyzing unit to reconstruct data and to calculate at least one of a correlation and a photon counting histogram for the desired region by use of the data on the fluorescence intensity, wherein a plurality of fluorescent images of the sample repetitively captured at predetermined time intervals are input to the image input unit; the storage unit stores data on the plurality of fluorescent images; and the extracting unit extracts, for each of the fluorescent images, data on fluorescence intensities in desired regions on the plurality of fluorescent images from the data on the plurality of fluorescent images stored in the storage unit.