Disclosed is a modified glucose dehydrogenases that has dramatically increased productivity in Escherichia coli and dramatically increased thermal stability, which is obtained by introducing specific amino acid mutations to glucose dehydrogenase derived from Botryotinia fuckeliana. Also disclosed is a modified glucose dehydrogenases that has dramatically increased productivity in E. coli and dramatically increased thermal stability, which is obtained by replacing two amino acid residues in glucose dehydrogenase of fungal origin with cysteine residues. The novel glucose dehydrogenase has a low reactivity to xylose.