PURPOSE: To homogeneously disperse fibers having long lengths and a small disaggregation ability and produce an uniform sheet having a good formation by a wet paper-producing method by subjecting a slurry comprising the fibers, water and a surfactant having a high foamability to a specific treatment.
CONSTITUTION: A slurry comprising fibers, water and a surfactant having a high foamability (e.g. a sodium alkylbenzenesulfonate) is subjected to a strong mechanical treatment to foam the slurry. The treatment is continued to disaggregate and disperse the fibers in the slurry. The slurry is mixed with a highly viscous solution (e.g. a CMC aqueous solution) and subsequently with a defoaming agent to defoam the slurry. The slurry is finally subjected to a paper-producing process. The mechanical treatment method is preferably a method in which the slurry is strongly stirred with a high speed mixer, etc., and a method in which air is blown into the slurry at a high speed.