An electric power supply circuit includes a switching element (S) for causing a short-circuit for output power of a diode bridge circuit (12), a zero-cross detector section (5a) for detecting a point at which an input voltage reaches a level equal to or lower than a reference level, a timer section (5d) for starting a count upon the detection by the zero-cross detector section (5a), and a PAM waveform output section (5c) for causing the switching element (S) to perform switching with a predetermined output timing so that a waveform of the input current is caused to approximate to a sine wave. The circuit further includes a correction section (5e) for correcting, when a difference between a detection interval from detection to detection by the zero-cross detector section (5a), and an average value for detection intervals up to current detection occurs, an initial value of the count of the timer section (5d) according to the difference.