An apparatus and a method for modifying the surface of a polymer powder utilizes a rotational ultrasonic treatment that pulverizes polymer materials, such as rubber, waste rubber, and plastics, and modifies the surface, so that the polymer materials can be recycled more efficiently. A hopper feeds the pulverized polymer powder. A rotor which is linked to the bottom of the hopper as an integrated body, is linked to a driving mechanism through a power transfer device, and rotates drive. A rotating disk is linked to the bottom of the rotor as an integrated body, and is provided with a downsloped plane. A shaft extends through the hopper, the rotor, and the rotating disk, and discharges the polymer powder fed from the hopper out of the bottom of the rotating disk. An ultrasonic vibrator is positioned at the bottom of the rotating disk, and modifies the polymer powder fed by the shaft using ultrasonic waves.