Abstract: A system of detecting a change in the charge put in a metallurgical furnace or the like wherein an magnetic field generator and a magnetic sensing section of a magnetometer arranged along the central axis of the exciting magnetic field of the said magnetic field generator are fitted in place on and/or inserted into a hole of the wall of such a vessel, including a metallurgical furnace or the like, as is enclosed with the said wall, such a change in the exciting magnetic flux passing through the said magnetic sensing section as is given birth by the movement of the charge is picked up in the form of electrical signals, and, the movement, the velocity, the rate of travel, the thickness of the layer, fluctuations in the shape of the layer, the circumferential distribution, the classification, and so forth, of the said charge are enabled to be properly detected in an optional manner through corresponding changes in the said electrical signals.