To provide a sensor input device capable of sending the detected information of a sensor as an electric signal disregard of whether a sensor to be connected is an internal power source type or an external power source type.

The sensor input device 2 for sending the detected information of a sensor 1 as an electric signal is provided with a power supplying means 4 having a power source for supplying power to the sensor 1, a switch means 5 for supplying power from the means 4 to the sensor or cutting off it, and a voltage judging means 3 for closing the means 5 at the time of detecting non-voltage from the sensor 1 when the means 5 is open in the detecting state of the sensor 1 and for opening the means 5 at the time of detecting voltage output from the sensor 1.