To make it possible to remove easily deposits built on a screen and further repair an anti-contaminant paint on the surface of the screen and paint the surface once again.

A ring-shaped training board 3 having a hole in similar shape with a surrounding shape of a main body 2 is mounted like a horizontal collar around the uppermost part of a cylinder-shaped main body 2 whose side surface is connected to an intake pipe 1. A cover 4 is laid out in the upper part of the training board 3 so that an intake spacing may be provided between the cover 4 and the training board 3. A main screen 5 is mounted between the training board 3 and the cover 4. Furthermore, a dividable cylinder-shaped sub-screen 6 is removably set up.