In a dielectric element, the side faces are roughened so that the surface roughness Ra is 15 nm or greater. By this means, the area of contact between a glass epoxy resin substrate and insulating material is increased, adhesion with resin substrates is improved, and strength and reliability can be enhanced when buried between two resin substrates. In the dielectric element, the surface roughness Ra of side surfaces is 5000 nm or less, so that when burying the dielectric element between a glass epoxy resin substrate and insulating material, the occurrence of air bubbles between the surface of the dielectric element and the resin can be prevented.