The invention relates to a device and to a method for determining the position for a working part of a tool on a working machine with a position-determining apparatus (2, 4, 5, 6; 2, 4a, 4b, 5, 6; 31, 33, 49, 50, 51, 1,53). At least one detector equipment (4, 5, 6; 4a, 4b, 5, 6; 31, 33; 49, 50, 51, 53) is placed at a defined place on the working machine (3; 52) in order to determine the position of this position in a fixed coordinate system. At least one positional relationship device (11) determines the positional relation of the working part in relation to the detector equipment in a machine-based coordinate system. A calculating device (20) calculates, with signals from the position-determining apparatus and the positional relationship device, the position of the working part in the fixed coordinate system. The position-determining apparatus comprises an inclination- and orientation-measuring device (5, 20; 4a, 4b, 20; 31, 20; 51, 20) so that the apparatus measures both the instantaneous position and orientation of said position of the working machine in the fixed coordinate system. The calculating device (20) converts the measuring result from the position-determining apparatus and the positional relationship device in order to give the instantaneous position and/or orientation of the working part in the fixed coordinate system.