PURPOSE: To maintain traveling safety at time of straight driving by installing each rolling wheel at the forefront to be liftably selected to a position where the lower end comes to be flush with other rolling wheel groups and a position where it relatively goes up by itself.
CONSTITUTION: At time of straight driving, a forefront side 4b is fixed to a position where it comes to be flush with other rolling wheel groups 4 by extension of a hydraulic cylinder 15, and longitudinal length of a crawler grounding part is lengthened whereby stable travel is performed. At time of body turning, the rolling wheel 4b is made to go up by contraction of the hydraulic cylinder 15 and thereby this crawler grounding part is shortened as far as a length portion equivalent to a distance between this rolling wheel 4b and each rear adjacent rolling wheel 4, and thus scarifying resistance is made smaller as much as possible.
DOI YOSHIAKI
KONISHI YOSHIAKI
