To provide a riding paddy field working machine capable of steering lightly by automatic switching operation by a rear wheel side clutch, and heightening the turning performance in a type of a machine with a comparatively small number of working threads.

This paddy field working machine is provided with a automatic side clutch operating mechanism for driving right and left steered front wheels through a differential gear, driving right and left unsteered rear wheels 2 through the side clutch and disconnecting the side clutch corresponding to the turning inside rear wheel 2 interlocking with steering the front wheels 1 at a preset angle or more. The maximum steering angle of the front wheels 1 is set to the space between the right and left front wheels 1, the space between the right and left rear wheels 2, and the space between the front and rear wheels so that with the turning inside front wheel steered at maximum, the turning radius R1 of a central area between the right and left front wheels 1 becomes smaller than the turning radius R2 of the turning outside rear wheel 2.