When an underwater ultrasonic wave is emitted toward an air-water interface, the water surface rises and droplets are generated from the formed fountain. The rising process of water surface was numerically investigated for better understanding the mechanism of ultrasonic fountain prior to the atomization. To analyze the water surface rising that occurs in a very short time, it is necessary to simulate the rapid increase of acoustic radiation pressure and the rapid development of acoustic streaming. Therefore, the direct numerical simulation based on compressible fluid dynamics was carried out. The water surface rising as observed in the formation process of ultrasonic fountain was successfully reproduced. In the region between sound source and water surface, standing wave is established and acoustic kinetic energy density increases significantly while water surface rises with acceleration. The kinetic energy density is associated with the acoustic radiation pressure acted on free surface based on the theory of Yosioka-Kawasima (1955). After the rising speed becomes to be constant, the standing wave fades and the kinetic energy density decreases. These results suggest that the acoustic radiation pressure acted on water surface increases significantly due to temporary resonance and water surface rises rapidly. By drawing a fluid due to rapid rising of water surface, acoustic streaming is induced toward the risen region.