Measurement of pulp swelling degree by centrifugal force is a method for evaluating the beatability of pulp. It is known that there is a close relationship between water retention and strength of paper. Water retention is measured by centrifugally separating water retained in pulp from free water in and between fibers. Put 0.5g (O.D.) of pulp slurry in the metallic pulp lined with wire, and scatter water. Then, the specimen is taken out from the filter and dried, and its mass is measured. Water retention is calculated from a formula.