A resin substrate includes a base portion including one first resin sheet made of a thermoplastic resin as a main material or a stack of two or more first resin sheets each made of a thermoplastic resin as a main material, the base portion including a main surface, and first and second connecting conductors provided on the main surface of the base portion and spaced away from each other. The base portion includes a convex portion separating the first and second connecting conductors on the main surface by a second resin sheet disposed at a position on a surface of the base portion or inside the base portion. The second resin sheet is made of the same material as the first resin sheet.