Disclosed is an active power factor correction integrated circuit for a boost converter, comprising a bias voltage generator coupled to an external power source through a first pin, for generating internal bias voltages used for the integrated circuit; a zero crossing detector coupled magnetically to the inductor through a second pin, for detecting a time at which a voltage across the inductor is zero to provide a zero crossing detection signal; an oscillator reset by the zero crossing detection signal for generating a pulse signal; a flip-flop for generating a first control signal in response to the zero crossing detection signal or the pulse signal; a switching element responsive to the first control signal for enabling a boosted voltage to be provided to the load; an over-current detector for generating an over-current signal when a current flowing through the switching element is over a predetermined value; and a voltage variation detector for detecting variation of a load voltage to generate a variation detection signal and generating a second control signal enabling the boosted voltage to flow through the switching element to a ground in response to both the variation detection signal and the over-current signal. With the integrated circuit, the number of the IC pin and the number of the peripheral components thereof may be considerably reduced.