Tool change apparatus for a machine tool

A tool change apparatus for a machine tool, comprising a tool holder receiving means which is provided on a spindle, a tool holder which can be fitted into said tool holder receiving means and which carries a tool, a change arm which engages said tool holder in a tool change operation, and an automatic actuating means which actuates a clamping means for connecting said tool holder to said tool holder receiving means, wherein said tool holder has a cylindrical portion for engagement of said change arm and can be fitted into said tool holder receiving means in the axial direction of said cylindrical portion, wherein provided in said cylindrical portion is a radially extending screwthreaded bore, wherein provided at the end of said change arm is a change head which is movable radially with respect to an axis of said cylindrical portion and which is provided with a prism-shaped centering recess at its outer end which is towards said tool holder, and wherein provided in said change head is a connecting pin which extends in the center of said centering recess in the radial direction of movement of said change head and which can be driven by motor means in two opposite directions of rotation and which is limitedly displaceable in its axial direction in said change head and which is provided at its free end with a male screwthread which fits into said screwthreaded bore.