PURPOSE: To decrease the number of insulators and to increase a mounting density of a storing board by converting a parallel data signal to a serial data signal, and thereafter, insulating it from an electric circuit of a contact side by the insulator.

CONSTITUTION: An opening and closing state of each contact 1 is converted to an electric signal by an input interface 2, and subsequently, it is converted to a serial signal by a parallel-series converter 5. Thereafter, said signal is led to a series-parallel converter 6 through an insulator 3, and its output signal is applied to a computer through a data gate 4 as a signal for showing an opening and closing state of each contact 1. The computer opens the gate when a gate control signal is applied to the data gate 4, and reads the data of each contact 1.