PURPOSE: To provide a rotary type screening device for grit which is capable of sieving substance having difference in specific gravity and easy in discharge of residue and small in load on a driving system.

CONSTITUTION: A screen part 15 is formed of a wedge wire wherein holes or gaps are bored and arranged in the outer circumference. A cylindrical trommel 11 having the screen part 15 is horizontally arranged and rotated by a rotary driver 19 and also a spiral blade 16 is fixed in the inner circumference of this trommel 11. Residue such as substance having small specific gravity is forcedly discharged by the spiral blade 16 by utilizing its lead angle. Thereby the need for obliquely providing the trommel 11 is eliminated. Thrust force is not generated in the rotary driver 19 and the speed of rotation of the trommel 11 is decided by the physical properties of sand and the design conditions are relaxed.