An image processing device which generates an image where a target object can be discriminated from an object other than the target object. An image processor (15), for echo signals read from a sweep memory (14), calculates a ratio of echo signals indicating a predetermined level or higher among the echo signals of a predetermined number of samples, and generates image data having a display element according to the calculated ratio. This ratio indicates a lower value for an object more isolated and a higher value for an object existing as a larger mass. The image processor (15)acquires color values according to the calculated ratio. Since the target object, such as a ship, is an isolated object and the ratio becomes low, the color values indicate red, and since inland is an object existing as a large mass and the ratio becomes high, the color values indicate green.