The present invention provides a photosensor device, which can cancel a dark current in 1-2 milliseconds. This photosensor device utilizes a small capacitor to quickly accumulate and transform the dark current to a dark-current voltage. Based on the dark-current voltage and an environment temperature, a calibration voltage can be obtained. By cancelling the calibration voltage from the sensed voltage to get a light voltage, which can be amplified to a lux signal. The process is very quick and sensitive, so the photosensor device can be used in an environment under a low luminance.