To provide a surface modifying method and the device by performing a peening process without any contact between a workpiece to be modified and a vibration plate, to reduce a reaction force applied to the vibration plate and need no solid shot material used for other peening methods, resulting in a decreased cost, no need to collect peening material and superior executing performance.

The device is provided with a high-frequency vibration generating device 1 which generates vibration of high-frequency, a vibration plate 2 which connects to the high-frequency vibration generating device 1 and vibrates at a high-frequency, a supportive device 4 which supports them so that a surface of the vibration plate 2 opposes in parallel with a surface of a workpiece to be modified 3, and a fluid retaining device which keeps a fluid 5 between the vibration plate 2 and the surface 3a of the workpiece to be modified 3.