A power conversion apparatus includes a converter having an input power source Vin, a reactor L1, a switching element Q1, and a rectifying element D1, a smoothing capacitor C1 connected to an output terminal of the converter, and a controller 10b to turn on/off the switching element and thereby control power to be outputted from the converter. The controller has a pulse generator 15 to generate a pulse signal according to an input voltage to the converter and an output voltage from the converter, the pulse signal being used to turn on/off the switching element. The controller also has an adjuster 18 to mask an ON time of the pulse signal for a predetermined time and thereby provide the pulse signal with an adjusted ON time, the adjusted ON time determining a duty ratio at which the switching element is turned on/off.