A switch device and method is disclosed that is capable of switching wavelength division multiplexed optical signals. The casing includes a first rabbet at an end flange in which is mounted a corresponding flange of the inner shell. The method for preparing fatty acid alkyl ester comprises the step of carrying out an esterification reaction of fatty acid raw material with alcohol in the presence of metal catalyst. The control means moves down a nozzle in sync with the time when the nozzle has finished passing over each obstacle after an electronic component has been photographed by a component camera. If this is the case, then a numeric analysis is performed. It is endeavoured to achieve a good efficiency combined with a simple assembly.