PURPOSE: To eliminate the need for post treatment such as dehydration of a product, to reduce a running cost and to enable sepn. with high accuracy, by electifying powder to be screened frictionally with a rotary type electrifying device, and separating the powder electrostatically according to the quantity of the electrification.

CONSTITUTION: The powder to be screened, which is chaged into an inside cylinder 53, which is a rotary wall body, through a supply port 54 receives an impact by the rotating force of said cylinder and is accelerated in the direction of an outside cylinder 51, which is a stationary wall, so as to collide against the inside wall of the cylinder 51. The powder subjected repeatedly to such operation receives the frictional electric charge corresponding to the component thereof and is discharged through a discharge port 55. The powder is separated accordig to the quantity of the electric charge and polarity of the charged particles in an electrostatic sepn. chamber consisting of parallel electrode plates which are applied with DC high voltage and are disposed in the perpendicular direction. The efficiency may be farther enhanced in the rotary type electrifying device by disposing the stationary walls and rotating walls in multiple stages.