As the first conductive paste, a paste is used which is made by adding an organic solvent to powder of alloy in which a plurality of atoms keep a given crystal structure constant. As the second conductive paste, a paste is used which is made by adding an organic solvent to powder of metal different in kind from the alloy. In a step of making the stack body, cavities are formed in the stack body. In a uniting step, the cavities work to facilitate flow of thermoplastic resin to absorb pressure acting in a direction different from a direction in which pressure exerted on the first conductive paste to unite the stack body, thereby resulting in an increase in pressure for the uniting to solid-state sinter the first conductive paste to make the first layer-to-layer connecting member.