The present invention relates to a downhole driving unit (11) for insertion into a well, comprising a driving unit housing (51), an arm assembly (60) movable between a retracted position and a projecting position in relation to the driving unit housing, an arm activation assembly (41) arranged in the driving unit housing for moving the arm assembly between the retracted position and the projecting position and a wheel assembly (90) comprising a stationary part (91) and a rotational part (92), the stationary part being connected with or forming part of the arm assembly and being rotatably connected with a rotational part. The wheel assembly comprises a hydraulic motor comprising a hydraulic motor housing (93) and a rotatable section (84) connected with the rotational part for rotating part of the wheel assembly. Furthermore, the present invention relates to a downhole system comprising said driving unit and to use of such driving unit.