Temperature measuring device for determining a medium temperature via the temperature of a measuring point on a surface enclosing the medium, comprising at least one measuring sensor and at least one reference sensor as well as measured value processing means, which is connected to the measuring sensor via a first supply line and to the reference sensor via a second supply line, wherein - the first and second supply line (13, 14) are each formed with an outer sheath, the outer sheath enclosing at least two inner conductors, - the at least one measuring sensor is connected to the inner conductors of the first supply line and the at least one reference sensor is connected to the inner conductors of the second supply line, - the outer sheath of the first supply line is connected to the outer sheath of the second supply line near the measuring point on the surface enclosing the medium by means of at least one coupling element, the measuring sensor and the reference sensor being thermally connected to the same thermally conductive coupling element at different distances, - the at least one measuring sensor and the at least one reference sensor are arranged between the surface enclosing the medium and the coupling element, and - the thermal resistance between the at least one measuring sensor and the coupling element is greater than the thermal resistance between the at least one reference sensor and the coupling element, and in that the thermal resistance between the measuring sensor and the measuring point on the surface enclosing the medium is smaller than the thermal resistance between the reference sensor and the measuring point on the surface enclosing the medium, characterized in that the first and second supply line (13, 14) are each designed as a mineral-insulated sheathed cable with an outer sheath made of metal, the at least two inner conductors being insulated from the outer sheath with highly compressed metal oxide powder, at least one further reference sensor being arranged on the main thermal connection path between the measuring point and the environment. - the first and second supply line (13, 14) are each formed with an outer sheath, the outer sheath enclosing at least two inner conductors, - the at least one measuring sensor is connected to the inner conductors of the first supply line and the at least one reference sensor is connected to the inner conductors of the second supply line, - the outer sheath of the first supply line is connected to the outer sheath of the second supply line near the measuring point on the surface enclosing the medium by means of at least one coupling element, the measuring sensor and the reference sensor being thermally connected to the same thermally conductive coupling element at different distances, - the at least one measuring sensor and the at least one reference sensor are arranged between the surface enclosing the medium and the coupling element, and - the thermal resistance between the at least one measuring sensor and the coupling element is greater than the thermal resistance between the at least one reference sensor and the coupling element, and in that the thermal resistance between the measuring sensor and the measuring point on the surface enclosing the medium is smaller than the thermal resistance between the reference sensor and the measuring point on the surface enclosing the medium, characterized in that the first and second supply line (13, 14) are each designed as a mineral-insulated sheathed cable with an outer sheath made of metal, the at least two inner conductors being insulated from the outer sheath with highly compressed metal oxide powder, at least one further reference sensor being arranged on the main thermal connection path between the measuring point and the environment.