PURPOSE: To control a transmission equipment while transparent-transmitting signals without using the control signal of RS-232C.

CONSTITUTION: An information processor 110 is provided with a storage means 111, an input/output means 112, an instruction forming means 113, a connecting means 114, and a control means 115 for controlling these respective means, adds the instruction for controlling a transmission equipment 120 at the end of the data of the storage means 111 by the instruction forming means 113, and transmits it to the transmission equipment 120. The transmission equipment 120 is provided with a connecting means 121, an instruction extracting means 122, an instruction analyzing means 123, a storage means 124, a transmission means 125, and a control means 126 for controlling these respective means, analyzes the instruction part extracted from the data from the information processor 110 with the instruction extracting means 122 by the instruction analyzing means 123, and also stores the remaining data in the storage means 124. Then, it is transmitted to other transmission equipments by the transmission means 125.