Provided are an image processor, an image processing method, and an endoscope system that calculates diagnosis support parameters on the basis of the state of blood vessels of an observation object. The image processor (65) includes an image acquisition unit (81) that acquires an endoscopic image, a blood vessel extraction unit (82) that extracts blood vessels, using the endoscopic image, a blood vessel information calculation unit (83), and a blood vessel parameter calculation unit (84). The blood vessel information calculation unit (83) calculates a plurality of items of blood vessel information including at least two or more among the number of pieces, the number of branches, a branch angle, a distance between branch points, the number of intersections, thickness, a change in thickness, the degree of complexity of a change in thickness, length, intervals, depth with a mucous membrane as a reference, a height difference, inclination, area, density, contrast, color, a change in color, the degree of meandering, blood concentration, the degree of oxygen saturation, a percentage of arteries, a percentage of veins, the concentration of an administered pigment, a traveling pattern, and a blood flow rate, in terms of the blood vessels. The blood vessel parameter calculation unit (84) calculates blood vessel parameters by calculating using the plurality of items of blood vessel information.
