The purpose is to provide an image generating device which generates a synthesized image from which one is able to intuitively grasp a relation between an image and a traveling position of a water-surface movable body. The image generating device includes processing circuitry. The processing circuitry acquires attitude information indicative of an attitude of a camera or a ship where the camera is installed. The processing circuitry acquires a traveling route of the ship based on a detection result of at least one of a position and a direction of the ship. The processing circuitry generates traveling route display data based on the attitude information and the traveling route. The processing circuitry generates a synthesized image in which the traveling route display data is synthesized with an image outputted from the camera.