To reduce the installation cost for pulp-separation after the production of enzyme and its running costs by producing enzymes, as a part of the pulp in paper production is used as a culture medium for enzyme production and adding the pulp and the enzyme in the culture mixture to the pulp production process.

A microorganism is cultured by using pulp in a bleaching step, for example, oxygen bleaching step, hydrogen peroxide bleaching step, peroxide bleaching step or ozone bleaching step in the production of pulp for paper making and using the product pulp after completion of bleaching step as a culture medium to produce enzymes, for example, cellulase or the like. The pulp and the enzymes included in the culture mixture are, directly without separation, added to the pulp for paper making before at least one or more the bleaching steps, for example, the oxygen-bleaching step, the hydrogen peroxide bleaching step, the ozone bleaching step, the hypo bleaching step, the chlorine bleaching step, the chlorine dioxide bleaching step and the enzyme bleaching step to effect the enzymatic treatment of the pulp for paper making.