The invention disclose a hydrogen fluoride containing composition comprising hydrogen fluoride and a compound which is liquid in the standard state (25° C., 1 atmosphere) and has a boiling point of 120° C. or more and pka of 12 or more at 25° C., and use of the composition for a fluorination agent. The compound which can be preferably used is represented by the formula (1): wherein R1 to R4 are a substituted or unsubstituted alkyl or aryl group and can be the same or different, and R1 or R2 or R3 and R4 can bond to form a ring having a nitrogen atom or a nitrogen atom and other hetero atom, or R1 and R3 can bond to form a ring having a nitrogen atom or a nitrogen atom and other hetero atom. The fluorination agent of the invention exerts effect with a similar reaction mechanism to hydrogen fluoride, can be applied to the halogen exchange reaction of a halogen containing organic compound, and can produce a fluorine containing compound with safety and ease without specific equipment or technique.