PURPOSE: To save the storage device and to simplify the system by designating a client terminal equipment through the designation of a LAN address with an ISDN sub address and converting the subaddress into the LAN address by a predetermined procedure so as to eliminate the need for a conversion table.

CONSTITUTION: In the system in which transmission reception of data between a facsimile equipment 10 connecting to a WAN 8 and a client 9 connecting to a LAN are conducted by using a facsimile server equipment 1, the client 9 is designated by using an ISDN subaddress. In this case, the subaddress is expressed in a numeral of decimal fixed number of digits in a form of giving zero to a head of binary, decimal or hexadecimal representation LAN address by an address conversion device 6 of the facsimile server 1 by arranging sequentially group numerals. Then the LAN address to designate a reception client is obtained from the ISDN subaddress and an overhead for an address cross reference table and table management is not required and the system is simplified.