A two-phase critical interleave PFC boost converter, includes a master-side control circuit configured to critically control a first switching element based on a master signal; and a slave-side control circuit configured to critically control a second switching element based on a slave-signal with a phase difference of 180° from the master signal. In the PFC boost converter, an off period generator of the master-side control circuit feeds an M_ON signal which is the same in waveform as the master signal to an on phase controller of the slave-side control circuit, and the slave-side control circuit determines the rising timing of the slave signal from the rising time of the master signal.