A temperature measuring device for determining a temperature of a medium via a temperature of a measuring point on a surface surrounding the medium includes: at least one measuring sensor; at least one reference sensor; and a measurement value processing means, which is connected via a first supply line to the at least one measuring sensor and via a second supply line to the at least one reference sensor. The first and second supply lines each are mineral-insulated sheathed lines with an outer sheath of metal, the outer sheath enclosing at least two inner conductors which are insulated from the outer sheath with highly compressed metal oxide powder. The at least one measuring sensor is connected to the at least two inner conductors of the first supply line and the at least one reference sensor is connected to the at least two inner conductors of the second supply line.