An isoxazolin-5-one derivative represented by the following formula (1) and an herbicide containing the isoxazolin-5-one derivative as an active ingredient are provided.In the formula (1), R1 represents a C1-C6 haloalkyl group, and R2 to R4 and X each represents a certain substituent or the like; and n represents an integer of 1 to 4, wherein X's may be different from each other when n represents an integer of 2 to 4.