PURPOSE: To enable tools to be rapidly interchanged by attaching removably the tool to a tool holder and removing the used tool to transfer it to an used container while providing an automatic interchanging device transfer the unused tool from a custody container for attaching it to the tool holder.

CONSTITUTION: Two transfer arms 70a, 70b of an automatic interchanging device are made pivotable. In the pivotable range of the arm are disposed a custody container 72 and unused container 74 above a tool holder section. The arms 70a, 70b are provided respectively with cylinders 94 having two long and short strokes, and tools can be clamped by claws at the end of a cylinder rod. The arm 70b is located right above the tool holder to remove an used tool clamped by the claws with the long stroke. The arm 70a then is on the custody container 72 and clamps an unused tool with the short stroke to carry out the cylinder operation of each arm while the arm is pivoted. The arms 70a, 70b are moved respectively onto the tool holder and used container 74 to complete the interchange of tools.