PURPOSE: To obtain a 1 to N type signal transmission equipment without requiring a large number of communication CPUs and to attain miniaturization and a low cost by constituting the device of a single communication control CPU and a simple selection circuit.

CONSTITUTION: When an input/output circuit 5-1 at the downstream of a switching circuit 13-1 is selected and set as the communication object of the CPU by the selection signals P1-Pn of the CPU12 by a select circuit 13, the signal P1 is set at 'L', and other P2-Pn at 'H's. The three-state buffers 23-2, 25-2-23-n, and 25-n of switching circuits 13-2-13-n are closed, and buffers 24-2-24-n are opened. Also, the three-state buffers 23-1 and 25-1 of the switching circuit 13-1 are opened, and the buffer 24-1 is closed, and only input from the downstream of the circuit 13-1 is inputted to the CPU12 via a signal line RX, and the output of the CPU is sent from only the buffer 25-1 set at an intermediate state to the signal input/output circuit 5-1, and only a slave unit 6-1 can communicate with the CPU, and other units can recognize that they are not the communication objects by the return of their own output signals. By performing the switching of the 'L' of the select circuit 13 and the selection signals P1-Pn sequentially, it is possible to perform 1 to N type transmission to perform communication control with (n) slave units only by a single CPU.