A power conversion apparatus capable of suppressing adverse effects of noise caused by crossing of wiring patterns on a wiring board mounting the apparatus thereon. The apparatus includes a transformer, a switching element connected to the transformer, a feedback rectification circuit, and a control circuit operable to control the switching element in response to a DC voltage from the feedback rectification circuit. A first wiring pattern electrically connecting the feedback rectification circuit and the control circuit is formed in one of two surface regions of the wiring board separated by an imaginary line running through a junction of the first wiring pattern and the feedback rectification circuit and a junction of the first wiring pattern and the control circuit, and a second wiring pattern electrically connecting the control circuit and the switching element is formed outside an area enclosed by the imaginary line and the first wiring pattern.