The present invention concerns a method for the lateral levelling equipment of a timber working head at a forestry machine with a hydraulic system for the driving and regulation of the functions of the forestry machine, which forestry machine comprises a chassis with a driver's cabin and an arm to which a timber working head is fixed jointed and in a manner that allows rotation, the working head comprising levelling equipment and a regulator for the control and regulation of the lateral angle of the working head relative to the vertical direction, an arrangement for the execution of the method, and a forestry machine for the use of the arrangement during the execution of the method.
