The present invention provides a
time of flight mass spectrometer having an
ion optics forming a multi-turn track, which is capable of time-focusing the ions while allowing the multi-turn track to be configured in an unlimited and highly variable manner. In a specific form of the invention, a reflector 9 is provided on the flight path between the position where the ions leave the loop
orbit P and the
ion detector 10 located outside the loop
orbit P, and the condition of the
electric field generated by the reflector 9 is appropriately determined. Thus, even if the ions cannot be well time-focused by the
ion optics 2 creating the sector-shaped electric fields 4 and 7, it is possible to compensate the time-focusing performance with the reflector 9 to achieve a good performance of time-focusing of the ion throughout the overall
system wherein the ions leave the
ion source 1 and finally reach the ion
detector 10. Thereby, the ions can reach the ion
detector 10 at approximately the same time even if the ions having the same
mass number have different levels of energy at the moment they leave the
ion source 1.