Method for producing fluorosulfonylimide ammonium salt

By reacting a compound [I] such as N- (chlorosulfonyl) -N- (fluorosulfonyl) imidoammonium salt with hydrogen fluoride, a compound such as N, N-di (fluorosulfonyl) imidoammonium salt [ II]. A compound [IV] such as an N, N-di (fluorosulfonyl) imide alkali metal salt is obtained by reacting the obtained compound [II] with an alkali metal compound or the like.