A subscriber input/output device of a high-speed packet switching system with a parallel common bus type is disclosed. The subscriber input/output device uses a coaxial cable to establish a star network of a radius of hundreds of meters, and the star network is arbitrated by a polling method to be used as a near communication network or an internal link network of a large scale communication system. The high-speed performance of 320 Mbps-class with a relatively simple medium access protocol for transmitting data through a common parallel bus is obtained, and broadcasting and multicasting are supported.