An object of the present invention is to provide a machine tool with a spindle chuck replacing function which has a simple configuration and enables a reduction in work replacement time. This heat treatment unit is improved from the conventional one in that it can give desired mechanical properties which are required by each part of metallic work requires without increasing the investment cost. The method also includes testing sending a test signal from the F1 fiber through the test splitter to the F2 fiber network, and replacing the test splitter after testing has been completed. A corresponding reading technique, where the data is \u201cunfolded\u201d is also described.