Disclosed are a novel hydantoin racemase and a process for producing an optically active N-carbamylamino acid or an optically active amino acid using the hydantoin racemase. A novel hydantoin racemase isolated and purified from Bacillus sp. Strain KNK519HR; a gene encoding the hydantoin racemase; a recombinant plasmid having the gene introduced therein; a transformant having the hydantoin racemase gene introduced therein; and a process for producing an optically active N-carbamylamino acid or an optically active amino acid characterized in that a 5-substituted hydantoin compound is treated in the presence of hydantoinase and N-carbamylamino acid amidohydrolase as well as the hydantoin racemase.