To set the length of a rotary tool (1a), to be thermally shrunk in place in a tool holder (7a), by means of an inductive heating device (15a), a setting device is provided with a positioning holder (61) for the rotary tool (1a), this positioning holder (61) being freely displaceable, but lockable, along a guide (35a) and its tool push-in movement into the thermally expanded tool holder (7a) being limited by a stop (71). The rotary tool (1a) bears with its tip (31a) against a stop (43a) of the positioning holder (61). By means of a length-measuring device (39a), the stop (71) limiting the push-in movement can be limited to a position in which the tip (31a) of the rotary tool (1a) is at a predetermined distance from a reference surface (33a) of a holder receptacle (17a), holding the tool holder (7a) during the shrink-fitting operation, or from a corresponding reference surface of the tool holder (7a).