A description is given of a heat flow meter which consists of an inner and an outer housing. The inner housing carries two heat sensors in a differential circuit, one of which is exposed to the radiation to be measured and the other is in thermal contact with the inner housing. The inner housing is connected to a cooling circuit which is controlled by a further thermostatic element connected in a thermally conductive fashion to the inner housing. The inner housing is arranged in the region of the rear wall of the outer housing. The walls of the outer housing are likewise connected to a cooling circuit. By means of the novel arrangement of the reference sensor and the control of the cooling circuit for the inner housing by means of a thermostatic element, as well as by means of the additional cooling of the outer housing, an especially great measuring accuracy is achieved.
