Abstract: Apparatus for measuring the temperature distribution along the inside walls of narrow, shaft-shaped spaces such as heating flues of coking and similar ovens using a radiation pyrometer with an evaluating arrangement, whereby a radiation optical system is disposed at one of the ends of the space and contains a mirror tiltable about an axis, for optical coverage of the entire length of the space and forwarding of the detected radiation into the path of rays to be evaluated, as well as a positioning arrangement for tilting the mirror over the area to be optically covered. Therewith a fixed mirror is arranged after the tilting mirror and the path of rays to be evaluated is focused to the end of a photoconductor, which, in a transportable and coolable measuring lance, is directed to an evaluating arrangement. The measuring lance can be coarsely and finely positioned by means of a carriage arrangement.