An apparatus for adjusting the rotation speed of a cross-cutting saw of a tree handling machine, especially grapple harvester is provided. The apparatus is arranged to control a hydraulic cylinder connected to the guide bar of the cross-cutting saw in a power transmitting way. A line communicating with the source of pressure medium and having an adjusting unit for adjusting the pressure of the cylinder is connected to the hydraulic cylinder. The system further includes a computing unit, and a rotation speed sensor in conjunction with the cross-cutting saw for measuring the rotational speed of the cross-cutting saw. The rotational speed sensor has a data transmitting connection with the computing unit arranged to control the adjusting unit according to the measured speed.