PURPOSE: To massively obtain the subject gene at a low cost by culturing a host cell transformed with a specific vector.

CONSTITUTION: Bacillus.subtilis IAI strain is extracted and separated to obtain (A) an inositol dehydrogenase gene having the formula or the substantially biologically same base sequence as the sequence of the formula. Subsequently, (B) a vector consisting of a plasmid pIOL05d15 containing the component A is obtained. A host, Escherichia coli, is transformed with the component B to obtain (C) Escherichia coli MV 1184 strain (FERM P-12531). The strain C is cultured in a medium containing a carbon source, a nitrogen source, etc., by an aeration culture method, etc., and (D) the cells are separated from the obtained culture product. The cells D is lysed and subsequently purified with a chromatograph such as Ultragel AcA-34 to provide the inositol dehydrogenase.