In a capacitor-mounted wiring board, a plurality of wiring layers each patterned in a required shape are stacked with insulating layers interposed therebetween and are connected to each other via conductors formed to pierce the insulating layers in the direction of thickness. A decoupling capacitor is electrically connected to a wiring layer used as a power supply line or a ground line in the vicinity of the wiring layer, and mounted such that, when a current is passed through the capacitor, the direction of the current is reversed to that of the current flowing through the relevant wiring layer.