PURPOSE: To make it possible to run even on a depressed ground by installing casters to the front and the rear, respectively, of a car body, and attaching one of these casters to a swing arm, and elastically supporting the swing arm rockably in vertical direction to the car body.

CONSTITUTION: When an unmanned carrier car 1 runs on the depressed place of ground GL, a first swing arm 13 rocks up and down with a pin 14 as a fulcrum, and presses wheels 3a and 3b against the ground, so it never turns out that the wheels 3a and 3b idle and become unable to run as before. Moreover, even in case that it runs on such place that the ground inclines in car width direction, it turns out that first and third swing arms 15 and 17 incline, corresponding to the inclination of the ground GL, so the inclination of the car body can be prevented.