The present invention provides a
time of flight mass spectrometer having a spiral flight path, whose
mass resolution can be appropriately changed with respect to the analysis object or other factor without any complicated alteration or addition of the
mechanical construction. In a specific form of the invention, the
mass spectrometer includes deflecting electrodes 20-23 located between semi-cylindrical electrodes 11 and 12 for making ions fly along a spiral path. The deflecting electrodes 20-23 generate deflecting electric fields for shifting the ions in the axial direction of the semi-cylindrical electrodes 11 and 12. The
voltage applied to the deflecting electrodes 20-23 is changed according to the mass resolution required. The deflecting electric fields are generated or removed with the change of the
voltage, which makes the ions fly either along a spiral path or in the same loop
orbit. The
flight distance of the ions can be controlled as desired by regulating the
voltage so that the ions fly in the loop
orbit an appropriate number of times. Thus, the mass resolution can be arbitrarily controlled.