This paper proposes a new smoothing technique for range images taken by a pulsed Time-of-Flight range finder. A Time-of-Flight range finder gives a range value from the sensor to the target by measuring the time until the emitted light is reflected on the target's surface and returned to the sensor. At the same time, the power of the reflected light is also measured as a side product of the range value for the most of range finders. The basic idea of the proposed technique is that the reflectance and range images are utilized for smoothing the range image corrupted by noise so that the detailed shape in the range image is preserved by applying the trilateral filter. Simulations and experiments using a laser range finder are successfully carried out for verifying the performance of the proposed technique.