PURPOSE: To effectively prevent the clogging of the vertical type net-like screening cylinder which is internally equipped with a grain lifting cylinder and is used to fine screening of grains.

CONSTITUTION: The net-like screening cylinder B erected in a screening chamber A is internally equipped with the grain lifting cylinder C and is so constituted that the grains can be finely screened while the grains are lifted between these cylinders. Both end edges 1, 2 which constitute the joint of the net-like screening cylinder B are superposed and adhered in such a manner that one end edge 2 to be positioned on the front side in a rotating direction (a) exists on the inner side. The front end 3a of a clogging preventive plate 3 having an inclined shape in the rotating direction (a) is constituted contactably with the outer peripheral surface of the net-like screening cylinder B. The front end 3a of the clogging preventive plate 3 is so formed that this end can be brought into pressurized contact with the outer peripheral surface of the net-like screening cylinder B. The clogging preventive plate 3 is formed to a curved shape in cross section so that its front end 3a can be brought into pressurized contact with the outer peripheral surface of the net-like screening cylinder B. The net-like screening cylinder B is bisected and the joints at the two points thereof are respectively bonded by spot welding.