Identification of a protein having an activity of oxidizing oleanane-type triterpene, and a gene encoding the protein, the protein and the gene, and use thereof are provided. For example, a protein having an activity of oxidizing oleanane-type triterpene obtained from a plant in the family Fabaceae, a gene encoding the protein and use thereof are provided. The protein is shown in, for example, SEQ ID NO: 4, 14 or 18, and the gene encoding the protein is shown in, for example, SEQ ID NO: 3, 13 or 17. A transformant into which the gene is introduced can be produced, and thereby a triterpene oxidase can be obtained.