The invention concerns a superconducting device used to measure temporally and spatially varying magnetic fields generated by sources inside the object to be investigated. The invention consists of a body divided into separate and easily interchangeable self-supporting modules, interconnected by connectors. The superconducting magnetometer or gradiometer elements (12) have been attached by means of connectors (11) to the cross-connection/support element (6); this element (6) is attached to a connecting element (4) by means of connectors as well. The connecting element (4) contains also the electric components (5) necessary for connecting the SQUIDs to the room temperature electronics (14). The connecting element (4) is attached to the neck plug (3), comprising a stiff thermal isolation preventing convection and a ribbon cable made of parallel twisted pairs. The element (3) is self-supporting and it forms an integral part of the magnetometer support structure. The cables in the neck plug have been made out of wires having a relatively high resistance in order to minimize the heat leak between the room temperature and the cryogenic environment of the magnetometers; the excess noise caused by the resistive leads has been compensated, for example by increasing the SQUID gain using positive feedback.