Abstract: An object of the present invention is to provide a novel substance that has a high reactivity as a fluorinating agent, is effectively used in various fluorination reactions, and is safely handled even in air. As the solution for achieving this object, the present invention provides a complex obtained by reacting bromine trifluoride with at least one metal halide selected from the group consisting of halogenated metals and halogenated hydrogen metals in a nonpolar solvent. This complex serves as a fluorinating agent that provides excellent fluorination performance and that is stable in air.