To enable a product having high degree of freedom in shapes, patterns, materials or the like to be formed, and a lightweight product to be inexpensively produced by using fiber formed into a muddy soil state by disaggregating a waste paper or the like in water.

A bagasse is added to a fiber in a muddy soil state obtained by disaggregating a waste paper or the like in water, and the obtained product is piled up on a planer or three-dimensional mold and dried. The dried product is separated from the mold to provide the objective paper product. When carrying out the piling-up treatment, the amounts to be piled up are changed according to the positions to form thin positions and thick positions with padding. The muddy fiber previously colored with a dye can be used, and a foreign matter such as a glass plate, a coral fragment, a driftwood, a seed of a tree, or the like can be inserted when the muddy fiber is piled up.