PURPOSE: To enable even a pen recorder which has only one pen to record the operation of many contacts by providing plural switch elements which are opened and closed corresponding to the respective states of objects of detection in binary states and resistance elements which are connected in series.

CONSTITUTION: The above device is equipped with the switch elements SW1 SW5 which are opened and closed corresponding to the respective states of the objects of detection in the binary states and the resistance elements R1 - R10 which are connected to the switch elements SW1 - SW5 in series. In this case, the resistance values of the respective resistance elements R1 - R10 are different from one another and the resistance values are set pn times (p: integer larger than 1, n: integer larger than 0) as large as a specific value (optional value). Therefore, a DC power source is connected, for example, across this parallel connection and its voltage drop is measured to detect the opening/ closure states of all the switch elements S1 - Sn. Consequently, data on the opening/closure states of many contacts can be outputted together to one output line.