A discharge lamp lighting apparatus includes a triangular signal oscillator, a first control part to compare the triangular signal with an error voltage between a reference voltage and a voltage corresponding to a first current passed through a secondary winding of a transformer and generate a first PWM control signal for turning on/off switching elements Qp1 and Qn1 with a phase difference of about 180 degrees and a pulse width corresponding to the first current, and a second control part to compare the triangular signal with an error voltage between a reference voltage and a voltage corresponding to a second current passed through a secondary winding S2 of a transformer T2 and turn on/off switching elements Qp2 and Qn2 in synchronization with the first PWM control signal with a phase difference of about 180 degrees and a pulse width corresponding to the second current.