A method of producing circuit boards, the circuit boards each including a first circuit board component and a second circuit board component, the second circuit board component having a bonding surface on which a wiring pattern finer than that of the first circuit board component is formed and to which the first circuit board component is bonded, the second circuit board component having a surface on which semiconductor elements are mounted that faces away from the bonding surface, characterized in that the method comprises: a second circuit board component preparation step of preparing the second circuit board component by performing a step of forming first electrodes on a support via a release layer for bonding to the semiconductor elements, a step of forming a multi-wiring layer, which is a laminate of a plurality of insulating resin layers and wiring layers, on the first electrodes, and a step of forming second electrodes on the multi-wiring layer for bonding to the first circuit board component; and a bonding step of bonding third electrodes of the first circuit board component to be connected to the second circuit board component, with the respective second electrodes of the second circuit board component; followed by: a resin supply step of filling a sealing resin in a gap between the first circuit board component and the second circuit board component; a resin curing step of curing the sealing resin; and a support release step of releasing the support from the second circuit board component via the release layer, which are performed through any one of the following sequences which are: the support release step, the resin supply step, and the resin curing step; the resin supply step, the support release step, and the resin curing step; and the resin supply step, a resin removal step of removing the sealing resin adhered to outer peripheries of the second circuit board component, the release layer, and the support, the resin curing step, and the support release step. a second circuit board component preparation step of preparing the second circuit board component by performing a step of forming first electrodes on a support via a release layer for bonding to the semiconductor elements, a step of forming a multi-wiring layer, which is a laminate of a plurality of insulating resin layers and wiring layers, on the first electrodes, and a step of forming second electrodes on the multi-wiring layer for bonding to the first circuit board component; and a bonding step of bonding third electrodes of the first circuit board component to be connected to the second circuit board component, with the respective second electrodes of the second circuit board component; followed by: a resin supply step of filling a sealing resin in a gap between the first circuit board component and the second circuit board component; a resin curing step of curing the sealing resin; and a support release step of releasing the support from the second circuit board component via the release layer, which are performed through any one of the following sequences which are: the support release step, the resin supply step, and the resin curing step; the resin supply step, the support release step, and the resin curing step; and the resin supply step, a resin removal step of removing the sealing resin adhered to outer peripheries of the second circuit board component, the release layer, and the support, the resin curing step, and the support release step. a resin supply step of filling a sealing resin in a gap between the first circuit board component and the second circuit board component; a resin curing step of curing the sealing resin; and a support release step of releasing the support from the second circuit board component via the release layer, which are performed through any one of the following sequences which are: the support release step, the resin supply step, and the resin curing step; the resin supply step, the support release step, and the resin curing step; and the resin supply step, a resin removal step of removing the sealing resin adhered to outer peripheries of the second circuit board component, the release layer, and the support, the resin curing step, and the support release step. the support release step, the resin supply step, and the resin curing step; the resin supply step, the support release step, and the resin curing step; and the resin supply step, a resin removal step of removing the sealing resin adhered to outer peripheries of the second circuit board component, the release layer, and the support, the resin curing step, and the support release step.