A sheet-conveying device designed to feed a sheet fed thereto through a fixing device toward a discharge unit includes first and second conveyance guides facing each other so as to define a sheet conveyance path and each having a conveying member designed to feed the sheet. An AWN extracts destination PBX node number from destination address information included in an N-ISDN SETUP message received from an AWN, decides the type of an audio CODEC corresponding to the PBX node number, and selects an audio CODEC corresponding to the type. N-Hydro-quaternary-nitrogen-onium tetrafluoroborate salts represented by the general formula generated accompanying the reaction are separated and recovered from the reaction mixture by means of depositing as crystals by the addition of solvents with a low affinity to the salts to the reaction mixture after the reaction.