A light source according to the present invention is for an exposure device of a multifunction peripheral and includes a multi-beam light source. Two laser diodes included in the multi-beam light source are individually driven by a laser driver. Reference signals Vref1 and Vref2 used to control the light emitting power of the laser diodes are individually generated by two reference signal generation circuits. The reference signals Vref1 and Vref2 are each generated by processing including digital calculation, and at least one of the reference signals Vref1 and Vref2 includes a component for correcting the relative output difference of the laser diodes.