This report describes the development of a prototype of small electronic private branch exchange for small and medium office use. The maximum capacity of the system is 36 extensions and 8 truck lines. The single line telephone used in the system can be either rotary dial type or DTMF push button type and the truck line can be either decade or DTMF signaling. No operator console is needed in the system and the major service feature are call back, last number redial, call pick, hold and transfer line etc. The system is Store Program Control of the whole system. Electronic switches are employed as the switching network with 11 internal up to 0.2 erlang per extension. The State Transition Language. The system has been testes and proved to be workable in office use.