The invention relates to an adhesion assisting agent-bearing metal foil comprising a layer of an adhesion assisting agent containing an epoxy resin as an indispensable component on a metal, wherein the adhesion assisting agent layer has a thickness of 0.1 to 10 .mu.m. The invention also relates to a printed wiring board being a multilayer wiring board having a plurality of layers, wherein an adhesion assisting agent layer is formed between insulating layers.