In an ion trap mass spectrometer including an ion trap space surrounded by a ring electrode and two end cap electrodes placed opposite each other with the ring electrode between them, a method of trapping object ions of a predetermined mass-to-charge ratio in the ion trap space more assuredly and effectively. An anode material for a secondary battery according to this invention comprises an Si oxide and at least one noble metal. The illumination member may also disable the target reference by not illuminating the at least one reference guide pattern in an illumination-off mode.