Method of manufacturing circuit board

To provide a technique of enabling reduction in dimension of an area having a large degree of roughness occurring around a via hole opening portion when manufacturing a circuit board having a small-diameter via hole. A method of manufacturing a circuit board comprises: (A) a step of laminating, on an inner layer board, a resin sheet having a supporting medium which contains a plastic film supporting medium and a resin composition layer joined to the plastic film support medium so that the resin composition layer is joined to the inner layer board; (B) a step of thermosetting the resin composition layer to form an insulation layer, the adhesion strength between the insulation layer and the plastic film supporting medium ranging from 2 to 18 gf/cm; (C) a step of irradiating the plastic film supporting medium with a laser beam from above to form a via hole having a top diameter of 40 [mu]m or less in the insulation layer; (D) a step of performing a desmear treatment; (E) a step of exfoliating the plastic film su