A tool fastening mechanism has a housing 2, in which a clamping opening 3 is embodied for receiving a tapering tool shaft clamping end 4 of a tool part 5. The clamping opening 3 tapers inward in the introduction direction of the clamping end 4 of a tool part 5, and furthermore the tapering sides are inclined toward one another in a plane extending perpendicular to the introduction direction, as a result of which the opening has a trapezoidal cross section, and the length of this cross section decreases away from the orifice of the clamping opening 3. The housing 2 furthermore has a transverse opening 7, which intersects the clamping opening 3 and in which a locking pin 8 is received. Upon introduction of a tool into the fastening mechanism, a tapering edge 20 of the pin 8 comes into engagement with a front edge 21 of an oblong hole 9, embodied in the clamping edge 4 of the tool part 5, and the resultant engagement action draws the clamping end 4 deeper into the clamping opening 3, while the pin 8 is driven farther into the transverse opening 7. The combination of the double tapering of the clamping opening 3 and the longitudinal locking accomplished by the locking pin 8 makes it possible to effectively restrict all six degrees of freedom of the tool part, within the production tolerances attainable by conventional mass-production methods.