PURPOSE: To prevent the deterioration of a SQUID and the corrosion of wirings and also prevent damage to the SQUID and the wirings by means of the thermal expansion stress of a cap.

CONSTITUTION: A SQUID 2 is arranged on the surface of a SQUID sensor and pin plugs 3A, 3B are arranged on the back. The SQUID sensor is provided with a printed board 1A formed of glass epoxy and a cap 5 formed of epoxy resin and adhered to the printed board 1 by using epoxy resin 6 for its peripheral edge to enclose the SQUID 2 and wirings 4A, 4B in no mutual contact.