[Problem] To effectively utilize plant residue such as soy bean skin, rapeseed meal, rice bran, rice husk, and cacao husk. [Solution] When forming sheet material from the mixture of burned plant material and fibrous material using a wet-process sheet production method, to use burned rice husk material, burned rice bran material, burned soy bean skin material, material generated by burning the inner skin of peanuts, or material generated by burning the side-walls of the water conducting tissue of plants, for the burned plant material; and for the fibrous material, to use either organic fibers derived from thermoplastic resins including polyethylene, polypropylene or other polyolefins, polyester, polyamide, vinyl chloride, polyacrylonitrile, polyvinyl chloride, and aramid, fiber derived from thermosetting resin including kynol, natural fibers such as cotton and wool, semi-synthetic fibers, glass fiber, inorganic fibers including carbon fiber, metal fibers with electroless plating applied on short fibers including iron, copper, stainless, steel, synthetic resins, and inorganic materials, or the combination of these short fibers.