A transformant obtained by introducing a DNA of (a1), (a2), or (a3) below, and (b) an alcohol dehydrogenase gene, into a bacterium of the genus Hydrogenophilus, can efficiently produce isobutanol utilizing carbon dioxide as a sole carbon source.
(a1) DNA which consists of a base sequence of SEQ ID NO: 1;
(a2) DNA which consists of a base sequence having 90% or more identity with SEQ ID NO: 1, the DNA encoding a polypeptide having 2-keto-acid decarboxylase activity;
(a3) DNA which hybridizes with a DNA consisting of a base sequence complementary to SEQ ID NO: 1 under stringent conditions, and which encodes a polypeptide having 2-keto-acid decarboxylase activity.