PURPOSE: To improve the straight-advance performance of a machin body by installing a speed change lever for exclusive use with which a pair of operating levers can be operated concurrently in the same direction and allowing a pair of operating levers to be equally swing-operated, independently of the individual difference between operators.

CONSTITUTION: A crawler traveling apparatus 6 is driven by a stepless speed change gear 15 constituted of a variable-capacity type hydraulic pump in which an oil passage is directly connected to a hydraulic motor 14 for driving the crawler traveling apparatus 6. The body of the stepless speed change gear 15 can be advanced or retreated or turned by independently adjusting the amount and the direction of discharge of working oil. In operation part, a pair of operating levers 16 are arranged, and the working-oil adjusting part of the stepless speed change gear 15 is interlocking-connected to a pair of operating levers 16. Another speed change lever 19 is supported onto the intermediate part of the operating lever 16 and fastened by a spring washer and a nut so that the swing posture can be arbitrarily set and maintained.