To make it easy to accommodate subscriber service signals for a communication system which converts the subscriber service signals using a wide frequency band exceeding 1 MHz from analog to digital, and multiplexes and transmits them by an optical fiber.

A subscriber service signal including an xDSL signal is converted from analog into digital first. Then sampling digital signals after conversion and a control signal are accommodated in a 1st multiplex signal and further 1st multiplex signals are multiplexed and processed on a time- division basis to generate a 2nd multiplex signal. The 2nd multiplex signal which is generated is transmitted through an optical fiber.