Terminals (11, 13) for electrical connection respectively have front end portions (11b, 13b) to be joined to a wiring board (20) with solder and base end portions (11a, 13a) drawn outside from a cover (7) made of heat-expanding material. In order for the base end portions to absorb stress countering the external force received from the cover subjected to thermal expansion due to the heat generated by an electromagnetic coil (5) by the deflection deformation of the intermediate portions (11c, 13c) of the terminals positioned closer to the cover than the wiring board 20 with the relay device mounted on the wiring board, the terminals are formed with a predetermined length of L′ in the extending direction of the terminals so that the length required for necessary flexibility is secured for the intermediate portions.