A network system providing secure service facility has a central control & management equipment to enable unified key management. The network includes a plurality of switching equipment and central control & management equipment, each of which includes encryption section. The encryption section of central management & control equipment encrypts; (a) a public key of switching equipment of a called party (i.e. terminating switching equipment); and, (b) a common key for encrypting message to be transferred between switching equipment. This is carried out each time a call requesting secure communication is originated. Then, the encrypted keys are delivered to the switching equipment of a calling party (i.e. originating switching equipment). Central management & control equipment maintains public keys of any switching equipment in a database.