PURPOSE: To reduce the number of signal lines, by converting an input signal to a serial signal in a key controller to transmit the serial signal and extracting clocks from receiving data in an operating part and converting the serial signal to a parallel signal to process the parallel signal.

CONSTITUTION: The signal inputted from a key matrix is converted to a serial signal consisting of a data clock signal by a key controller 3 and is sent from a keyboard part 1 to an operating part 11 through a signal line 4. In the operating part 11, a single shot 12 is triggered by the trailing edge of the signal to output a clock 20. The data clock signal is sampled by the fall of the clock 20 to convert the serial signal to a parallel signal in a serial-parallel converting part 13. A counter 14 counts the clock 20; and when the counted value reaches one- character components of pulses, an operation controller 15 is interrupted through line 19, and the counter 14 is reset through a line 18, and the interruption is released. Next, the controller 15 samples data on a data bus 16 by its own data read signal 17. Thus, the keyboard and the operating part are connected easily with a small number of signal lines.