PURPOSE: To permit a computer having only one port to simultaneously transmit data to plural printers by outputting a printer action signal for computer to the computer as long as even one individual printer action signal is inputted.

CONSTITUTION: Data outputted from a host computer 2 are distributed by a data distribution means 1 and are distributed to respective printers 31, 32 and 33. In this case, an individual BUSY signal 330 from the printer 33 goes to a LOW state last. Consequently, an individual printer action detection means 5 outputs the BUSY signal for computer to the host computer 2 until the BUSY signal 330 goes to the LOW state even if the individual BUSY signals 310 and 320 are in the LOW state. The BUSY signal for computer is not set to the LOW state until the BUSY signal 330 goes to the LOW state. Thus, data are smoothly transmitted from the host computer 2 to respective printers.