The first case made of metal and the second case made of resin seal the circuit substrate 130 hermetically by the adhesive seal material, an engaging elastic member having a hook part is stand up at an inclination angle θ of less than 90 degrees at the front of a plurality of pressing elastic members provided on the outer periphery of the second case, when the first case is mounted by the assembling jig, the engaging elastic member moves backward, when the first case is pushed further, the pressing elastic member is bent upward by the jig base, the hook part is engaged, when the jig is removed, the first case and the second case are pressed against each other by the restoring force of the pressing elastic member, when the adhesive seal material is dried and cured, the adhesion force thereof secures close contact integrity between the cases.