To determine the amount of rail wear, it is necessary to measure the rail cross-sectional profile. We developed a new device for this purpose which is composed of two beam units, two camera units and a computer unit by using the light-section method. Through laboratory and field tests of this device, we found the usefulness of interference filter to remove the influence of sunlight and the interference between the two beam units, determined the most appropriate geometrical relation between the beam units and camera units, selected the proper location of two camera units, and confirmed the measurement precision of 0.5 mm when the device is used for actual tracks.