throughout an entire outer periphery of the cylindrical screen 1 incidentally in the cylindrical screen 1 one end of each screen bar 2 at an upper side portion of the screen 1 is supported by a first end plate r 1 in a ring form and the other end of each screen bar 2 at the upper side portion of the screen 1 is supported by the member 3 formed in the ring form also in each of the screen bars 2 at a lower side portion of the screen one end thereof is supported by the member 3 formed in the ring form and the other end thereof is supported by a second end plate r 2 reference numeral 4 denotes an agitator formed outside the cylindrical screen 1 and by utilizing a change of pressure caused at front and rear sides of the agitator 4 by the rotation of the agitator 4 the screen cleaning operation for the screen 1 is carried out therefore according to the embodiment a papermaking material entered from a material inlet passage 5 is subjected to an agitating operation by the agitator 4 in a tank 6 and good fibers are guided to an outside of the tank 6 through the longitudinal slits s and an outlet passage 7 it is structured that the foreign substances can not pass through the longitudinal slits s to thereby remove the foreign substances from the papermaking material in this case the fibers are accumulated on the surface of the screen 1 such that a mat.