A drive assembly has a track frame, an idler, and a sprocket arranged substantially on a straight line that includes single track roller units disposed respectively closest to the idler and closest to the sprocket. The single track roller units each rotatably support a track roller at an end of an arm that is rockably attached at another end to the track frame. The single track roller units bear the vehicle body load at the distal end of the arm through elastic members. A double track roller unit is interposed between the single track roller units, and includes a first arm rockably attached at its end to the track frame and a second arm rockably attached at its central portion to another end of the first arm. The second arm rotatably supports paired front and rear track rollers at two ends thereof.