Disclosed are: a novel microorganism which can decompose a methylthiotriazine compound (particularly, simetryn, dimethametryn, prometryn), a chlorotriazine compound (particularly, simazine, atrazine, propazine) and a methoxytriazine compound (particularly, simeton, atraton, prometon) which have been frequently used as agrichemicals or the like; and a method for decomposing a methylthiotriazine compound, a chlorotriazine compound and/or a methoxytriazine compound by using the microorganism. Specifically disclosed are: a novel bacterium Nocardioides sp. strain MTD22 which is capable of decomposing a methylthiotriazine compound, a chlorotriazine compound and a methoxytriazine compound; and a method for decomposing a methylthiotriazine compound, a chlorotriazine compound and/or a methoxytriazine compound, particularly simetryn, dimethametryn, prometryn, simazine, atrazine, propazine, simeton, atraton and/or prometon, by using the microorganism.