A new lignin degradation product, a method for producing the same, and methods for producing a saccharide raw material and a monosaccharide raw material are provided.The method for producing the new lignin degradation product includes: (a first step) mixing 100 parts by mass of a powder, obtained by pulverizing a lignocellulosic raw material and defatting the resulting powder with an organic solvent, with aqueous hydrogen peroxide in an amount of 20 to 400 parts by mass in terms of hydrogen peroxide and heating the mixture for 5 to 120 minutes at a pressure of 0.1 to 1.5 MPa and a temperature of 80 to 200° C. while irradiating the mixture with microwaves; (a second step) separating insoluble matter from the aqueous hydrogen peroxide; (a third step) extracting the insoluble matter with a solvent to produce an extract; and (a fourth step) distilling the solvent away from the extract to yield a solubilized lignin as a residue. Further, a saccharide raw material composed mainly of a polysaccharide or a monosaccharide raw material is obtained by subjecting the liquid portion or the insoluble matter, respectively, obtained in the first step to a predetermined treatment.