An image obtainment apparatus images an observation target to obtain an ordinary image by illuminating the observation target with illumination light and by receiving, at an imaging device (22), reflection light reflected from the observation target. Further, the apparatus generates spectral estimation image signals of a predetermined wavelength by performing spectral image processing on image signals output from the imaging device (22). A spectral image processing unit (32) generates spectral estimation image signals of a specific wavelength related to an agent administered to the observation target, as spectral estimation image signals for obtaining luminance information, based on the image signals output from the imaging device (22). Further, a luminance information obtainment unit (34) obtains luminance information about each of the spectral estimation image signals for obtaining luminance information that have been generated at a predetermined time interval, and obtains a rate of change in the luminance information.
