PURPOSE: To reduce the abrasion of a tire due to slip when the tire travels on a curved road by allowing some among the axles of the connected passenger trains in multiaxle constitution to be self-steered in accordance with the road-surface resistance.

CONSTITUTION: Each knuckle pins 10 having a tire 7 is axially installed onto the both edges of an axle shaft 8 of a trailer 2 in turnable ways by use of a king pin 9. A roller bracket 16 is connected onto a knuckle arm 11 installed onto the knuckle 10 through a tie rod 15. A roller arm 14 is installed onto the axle shaft 8, permitting to be pressed by a chamber 25, and a roller 17 installed onto the roller bracket 16 is shifted rightward or leftward from the center position on steering, and when a car travels straight, the roller is allowed to contact with the center of the roller arm 14 so as to be returned to the center position.