The present invention provides a protein having an activity of oxidizing a dammarane-type triterpene, a gene encoding the same, and use of the protein and the gene. The present invention specifically relates to a protein obtainable from a plant belonging to the genus Glychyrrhiza, which has an activity of oxidizing a dammarane-type triterpene, a gene encoding the same, and use of the protein and the gene. The protein is shown in SEQ ID NO:1, 2, or 13, and the gene encoding the same is shown in SEQ ID NO:3, 4, or 14, respectively. Furthermore, a transformant into which the gene is introduced can be produced, by which a triterpene oxidase can be obtained.