A machine tool system includes a machine tool having a processing chamber covered by a cover and a door for covering or uncovering an opening formed on the cover; a stocker for being removably mountedon the machine tool to thereby define a storage space outside the processing chamber; and a robot having a movement range spanning the storage space and the processing chamber when the stocker is mounted on the machine tool. In the machine tool mentioned above, the stocker includes a safety fence that defines, in cooperation with the outer surface of the machine tool, a protective space when thestocker is mounted on the machine tool. The protective space is a space for accommodating the storage space.