An electronic ballast for a discharge lamp includes a predictive circuit and a correction circuit in addition to a power conversion circuit including an inverter circuit and a resonant circuit, a drive circuit and a frequency control circuit. The inverter circuit applies load voltage across a load circuit including the lamp via the resonant circuit. The predictive circuit predicts a resonance frequency of the combination of the resonant circuit and the load circuit after ignition of the lamp. The resonance frequency is predicted based on an input signal representing the load voltage in the period of time from the start of sweep of the inverter circuit's operating frequency through a time point immediately after ignition of the lamp. The correction circuit changes the end frequency of the sweep to the resonance frequency.