Abstract: The invention relates to a chassis structure for a working machine moving on a terrain, the chassis structure (40, 60) comprising a pair of front wheels and a pair of rear wheels supporting the frame (41 to 42, 61 to 62), and a controlled frame joint (63) between the frame parts (41, 42, 61, 62), when the frame is composed of two frame parts. The chassis structure (40, 60) further comprises a suspension (1a) controlled by actuators and arranged to move each wheel in a level transverse in relation to the frame. Each wheel is mounted rotatably and to turn by means of the actuators to the suspension, and each wheel is usually provided with hub motor means for drive transmission. The chassis structure (40, 60) can further comprise a pair of middle wheels for a second frame part (42, 62). In a method related to the chassis structure (40, 60) the forest machine can also be turned in place.