This tester readily screens pulp fibers through screens into groups by fiber length. It consists of four screening tanks with wire cloth of different mesh sizes and an injection tank. As water and pulp are poured into the tanks together at a certain flow rate, fibers run along on the water flow to be screened into the four tanks serially placed on steps. Agitators are provided to prevent fibers from being deposited on the screens. The component elements are coupled together with a V-shaped belt, simplifying the mechanism, and controlling noise.