PURPOSE: To simplify manufacture with a usual secondary seal process eliminated by synchronizing the atmospheric pressure in a furnace with the atmospheric pressure variation in the inside of a relay until sealing is completed in a high-temperature drying furnace when a relay main body is housed in a housing and the joining surface of a base and a case and a terminal protruded part are sealed with an adhesive.

CONSTITUTION: A hole insertedly passing plural terminals 5 is provided on a flat-plate- state base 1 composed of synthetic resin, an electromagnetic part 3 having contact parts 4 is attached to the inside of the base 1, and these are covered with a case 2 made of a similar synthetic resin. Then a high-temperature hardening resin 6 such as epoxy resin etc.,is applied to the engaged part of the base 1 and the case 2 and a terminal protruded part to be temporarily sealed, the resin 6 is put in the temperature-pressure control drying furnace 9 controlled with a control device 8, temperature is raised beyond a seal material hardening temperature, and then the resin 6 is hardened with the atmospheric pressure in a relay R risen. At that time the atmospheric pressure in the furnace 9 has been maintained until the resin 6 is stabilized, and then restored to normal atmospheric pressure. Thus the occurrence of sealing failure can be prevented.