An image processing apparatus includes: an image acquisition unit that acquires a plurality of endoscope images obtained by imaging an observation target at different times with an endoscope; a blood vessel extraction unit that extracts blood vessels of the observation target from the plurality of endoscope images; a blood vessel information calculation unit that calculates a plurality of pieces of blood vessel information for each of the blood vessels extracted from the endoscope images; a blood vessel parameter calculation unit that calculates a blood vessel parameter, which is relevant to the blood vessel extracted from each of the endoscope images, by calculation using the blood vessel information; and a blood vessel change index calculation unit that calculates a blood vessel change index, which indicates a temporal change of the blood vessel, using the blood vessel parameter.