This monosaccharide production method is a method for producing monosaccharides from biomass having a first step 3 in which a raw material biomass is pretreated in 65 to 85 (w/w) % sulfuric acid at a temperature of 30 to 70.degree. C., and a second step 4 in which the first step treatment product pretreated in the first step is subjected to saccharification treatment in 20 to 60 (w/w)% sulfuric acid at a temperature of 40 to 100.degree. C.