To obtain an epoxidizing catalyst capable of converting an olefin to a corresponding epoxide with high selectivity, and to provide an epoxidizing method.

The olefin is epoxidized by using the epoxidizing catalyst comprising a cyclic amide transition metal complex (1) represented by formula (1) (wherein R1, R2, R3, R4, R5 and R6 are each H, a 1-16C hydrocarbon group, a perfluoroalkyl group or a halogen atom, R7 is H or a 1-18C alkyl group, R8 is a 5-17C hydrocarbon group which may be substituted or a perfloroalkyl group, M is a transition metal, L is a ligant and Q is a paired ion). The epoxidizing method for an olefin uses the epoxidizing catalyst comprising (a) the cyclic amide transition metal complex (1) and (b) a peroxy oxidizing agent.