Disclosed is a low-cost parallel lighting system for discharge lamps for a surface light source, which reduces nonuniform brightness and static noise, and fulfills a requirement that lamp currents of individual cold-cathode fluorescent lamps should be uniform and stabilized. In a surface light source system having multiple discharge lamps, there is a module which lights the discharge lamps in parallel and whose input terminal and electrodes on an opposite side to that side of the discharge lamps which is connected to the module are driven by voltage waveforms different in phase by 180 degrees from each other, wherein an input terminal of an opposite phase of the surface light source system is connected to an inverter circuit having outputs of opposite phases via a single shunt transformer in such a way as to cancel out magnetic fluxes generated by currents respectively flowing in windings of the shunt transformer, whereby the resonance frequency of the inverter circuit having outputs of opposite phases is matched to balance the outputs.