To provide a sensor signal amplifying device of a simple constitution which is capable of stably amplifying a sensor signal without causing a fault due to a response delay of an input capacitor.

The device is equipped with the input capacitor which takes in the pulsed sensor signal outputted from a light-receiving IC for a photoelectric sensor, for instance, and an amplifier which amplifies and outputs the sensor signal taken in through the input capacitor, wherein particularly one end of a diode circuit formed by connecting a resistance and a diode in series is connected between the input capacitor and the amplifier. A prescribed voltage is impressed on the other end of the diode circuit so that a reference level of the sensor signal taken in through the input capacitor be held constant.