PURPOSE: To continuously and quickly measure the change of the gauge resulting from travels of trains, by detecting the gauge of rails by a laser displacement sensor mounted to a stabilizer fixed to a truck, and storing/displaying the track along with the positional data of a rotary distance sensor.

CONSTITUTION: A vehicle 1 ravels on rails 5, 6. A contact rotary distance sensor 7 for detecting the travel position and a stabilizer 8 are loaded on a truck 2. Laser displacement sensors 10, 11 mounted on the stabilizer 8 emit laser beams 12, 13 parallel to an axle 14 to the gauge corners of the rails 5, 6 during travel of the vehicle 1, detects reflected lights 15, 16 continuously and obtains the distance of the right and left rails 5 and 6, namely, the gauge continuously. The result is stored in an operating device 17 mounted on the vehicle 1. Moreover, the positional data from the rotary distance sensor 7 is also stored and displayed by a display device 18. Accordingly, the measurement results can be seen immediately, which contributes to the prevention of train accidents.