Abstract: A plurality of superconducting quantum interference magnetometers are provided corresponding to a plurality of channels. Each of the superconducting quantum interference magnetometers is accommodated in a cooling vessel and has a superconducting detection loop for interlinking with the unknown magnetic flux. A superconducting magnetic sensor is magnetically coupled to the superconducting detection loop for producing an output voltage pulse. A feedback circuit, supplied with the output voltage pulse from the superconducting magnetic sensor, produces a magnetic flux that counteracts the unknown magnetic flux in response to each output voltage pulse. A gate circuit is provided between the superconducting magnetic sensor and the feedback means for controlling the supplying of the output voltage pulse from the superconducting magnetic sensor to the feedback circuit. The gate circuit is supplied with a control signal and selectively passes the output voltage pulse in response to a logic level of the control signal.