A semiconductor laser driving circuit includes a light amount detector, a frequency determiner, and an initialization circuit. The light amount detector detects an amount of light emitted by a laser diode, and outputs a first voltage corresponding to the amount of light. The frequency determiner determines a frequency for determining a time period of a detecting operation to detect differential quantum efficiency of the laser diode. The initialization circuit performs an initialization operation to detect differential quantum efficiency of the laser diode with a variation of the time period of the initialization operation according to the frequency determined by the frequency determiner.