A tool holder module has a tool holder and a tool holder assembly jig. The tool holder assembly jig has a horizontal supporting seat. A flange recess is formed in the top surface of the horizontal supporting seat and is configured to accommodate a flange of the tool holder. The flange recess has two clamping portions, and each clamping portion protrudes from a respective one of two opposite surfaces of the flange recess and extends linearly from an opening of the flange recess toward a bottom of the flange recess. The two clamping portions are configured to engage with the two clamping recesses to prevent the tool holder from rotating relative to the horizontal supporting seat. The tool holder is selectively mounted on one of the vertical supporting seat and the horizontal supporting seat.