A packet switching apparatus is constructed by a basic module disposed in the apparatus casing and an additional module disposed on the outside of the apparatus casing. The basic module has a common processing function irrespective of an access method and a service type, an interface accommodating lines to be connected to the Internet, and a plurality of interface boards conformed to a specific access method by which a hardware scale may be small. Only the basic module functions as a packet switching apparatus, and a processing function peculiar to each access method and service type is executed by the additional module.