Abstract: Device for measuring the temperature of the material contained in a closed apparatus. Including a probe equipped with a sensitive thermocouple element mounted in a protective housing made of an electrically and thermally insulating material in contact with the material to be measured, the element is connected with a preamplification electronic circuit adjacent to it, and having an operational preamplifier connected with a couple of semiconductor switches and an integration circuit which probe is connected to means located at a distance from the apparatus for amplifying and processing the signal and associated with visualization, recording and control members.