Abstract: A device for controlling the level in a container of a liquid which will emit infra-red rays and particularly molten metal is described. The device comprises a housing, at least one longitudinal window at one end of the housing and arranged so that when in use it will overlook an edge of a container containing the liquid, the level of which is to be controlled; and at least one photo-element for sending out an electrical signal through said window to said liquid; at least one second window which is substantially punctiform and which overlooks a substantially constant portion of the liquid in the container and within the vertical field of adjustment; and a second photo-element in cooperation with the second window for sending out a pilot signal, and circuitry to correct the signal indicating the liquid level of the container by means of the pilot signal and for amplifying and comparing the signal coming from the correction circuit.