PURPOSE: To evade the contention in use of a printer, and to effectively use the printer, by coupling plural sets of main body parts, and a set of printer with a simple method.

CONSTITUTION: A three-state gate is provided between each of data transmitters 11∼11, and a data bus 13, and a signal control line RS setting a first level in a state where each of the data transmitters is connected, and the data bus 13 is not used, and a second level in the state where the data bus 13 is occuplied, is provided. And respective data transmitter 11, when desiring data transmission from its own equipment to a data sink 12, confirms the fact that the control signal line RS is set at the first level, and energizes the three-state gate, and sends the data, and also, changes the control signal line RS to the second level. In this way, only by providing one control signal line RS, it is possible hereafter to transmit the data to the data sink 12 such as the printer by the control of the main body part of a CRT part, etc., as evading the contention between other data transmitters and the data bus 13.