A power source device includes an oscillator generating a clock, a frequency division unit dividing the clock to output a pulse, a sequence generation unit generating sequences “N” with respect to each switching of the pulse, a frequency division ratio setting unit setting frequency division ratio, a switching element driven by the pulse, and a piezoelectric transformer outputting alternating high voltage from a secondary-side when a primary-side is applied with voltage. The generated sequence and the set frequency division ratio are compared to output the pulses of fractional-M, -M+1 frequencies. An average frequency division ratio of the pulses of fractional-M, -M+1 frequencies determined by (M×α)+(M+1)×β/(α+β), where α and β respectively represent the number of pulses of “M” and “M+1” per unit time. The average frequency division ratio and frequency division ratio become equal at a sequence generation cycle and approximated in a period shorter than the sequence generation cycle.