PROBLEM TO BE SOLVED: To introduce an axle box in a device for changing a wheel interval during unlocking surely, open and close a lock and change a track gage surely and provide at a low cost.
SOLUTION: A track gage changing means 10 formed by a long material alienates narrow/wide running rails 11, 12. Side guides 15 are projected along support stands 9, 9. Right and left guide areas (a), vertical guide areas (b), first balance guide areas (c), operation areas (d) and second balance guide areas (e) are formed in order towards the track gage changing area (f) from both ends of a track side device 13. Both ends of the side guide 15 are expanded in the area (a). The height of the running rail is made constant and the support stand 9 is descended as heading for the outside in the area (b). In the areas (c), (e), the side guides 15, 15 are parallel with a track center (o) and in the area (c), respective support stands 9 are vertically parallel with the running rails 11, 12 and in the area (e), the height of the support stand 9 is made constant and the rail alienate part is provided. In the area (d), the height difference between respective support stands 9 and running rails 11, 12 is enlarged as approaching to the area (f).