A method of manufacturing a resin multilayer substrate with a cavity, includes stacking insulation substrates including thermoplastic resins and thermocompression-bonding the insulation substrates. At least one of the insulation substrates is formed by affixing a peelable carrier film to one main surface of the insulation substrate, making a cut in the insulation substrate having the carrier film affixed thereto, the cut being designed to form the cavity, penetrating the insulation substrate in a thickness direction and not penetrating the carrier film in a thickness direction, and removing the carrier film and a portion of the insulation substrate that is cut out by the cut.