Device and method for fixing an image in which a vibrator, which generates ultrasonic waves by applying a voltage, and a horn connected thereto are arranged opposite a pressure roller with an endless belt passing between the horn and the pressure roller. Recording paper is carried between the belt and the pressure roller so that an image surface thereof is brought into contact with a rubber layer on the endless belt. Ultrasonic vibration is transmitted to the image surface of the traveling recording paper via the belt, thereby directly heating and melting toner so that the image is fixed on the recording paper.