To provide a resin composition excellent in electric properties and capable of forming fine via holes by laser when formed as a resin layer of the circuit board and to provide a resin layer excellent in electric properties and capable of forming fine via holes by laser and a carrier material and a circuit board each equipped with resin layer using the same.

The resin composition constitutes an insulating layer of a circuit board forming via holes by laser irradiation and the composition comprises a cyclic olefin resin having polymerizable functional groups on the side chains, an azide derivative as a laser processing property-imparting agent and a polymerization initiator. The resin layer is constituted of the resin composition. The carrier material having the resin layer forms the resin layer on at least one surface of the carrier material. The circuit board has the resin layer.