A resin filler preferably packed in recesses occurring in the surface of a wiring board or in through holes provided therein, and a structure of a highly reliable built-up multilayer printed wiring board filled with the same resin filler are proposed. This resin filler is a solventless resin filler to be packed in the recesses occurring in the surface of a wiring board or in the through holes provided therein, the resin filler being characterized in that the filler contains resin components of bisphenol type epoxy resin and a curing agent of imidazole, and an additive component of inorganic particles as necessary. A built-up multilayer printed wiring board using this resin filler is also proposed.