An ultrasonic wave applying liquid is supplied to one principal surface of a substrate while a liquid film of a first liquid being formed on another principal surface of the substrate. The ultrasonic wave applying liquid is obtained by applying ultrasonic waves to a second liquid. Ultrasonic vibration is transmitted to the other principal surface and the liquid film, thereby ultrasonically cleaning the other principal surface. The first liquid has a higher cavitation intensity, which is a stress per unit area acting on the substrate by cavitation caused in the liquid when ultrasonic waves are transmitted to the liquid present on the principal surface of the substrate, than the second liquid.