Signal light detection device and method

An electric signal generated by a photoelectric conversion element (104) is inputted into a comparator (120). The comparator (120) determines whether or not an electric signal outputted by an amplifier (110) is greater than or equal to a reference voltage and outputs a high signal when the electric signal is greater than or equal to the reference voltage. A reference voltage modification unit (130) raises the reference voltage once the comparator (120) determines that the electric signal is greater than or equal to the reference voltage and after a predetermined amount of time has elapsed. On the basis of the pulse width, which is the period from when the electric signal equals or rises above the reference voltage to when the electric signal equals or drops below the reference voltage, a signal processing device corrects the rising timing which is when the electric signal became greater than the reference voltage, thereby calculating the timing with which a signal light began to enter a photoelectric conversion unit (100).