The invention relates to a glucose dehydrogenase showing an NADP/NAD activity ratio, namely the value obtained by dividing the enzyme activity value obtained by using NADP as a coenzyme by the enzyme activity value obtained by using NAD as a coenzyme, of not lower than 300, to a gene coding therefor, and to a transformant harboring that gene. The enzyme of the invention is very high in NADP specificity and can be suitably used, for example, for NADPH production, for coenzyme regeneration in enzymatic reduction reactions, and in biosensors for glucose concentration measurements.