Accordingly, as illustrated in FIG. 14, the potential of the first electrode 121 with respect to the COM potential is a positive potential (+5 V) from time t1 to time t8, a negative potential (?5 V) from time t8 to time t13, the positive potential (+5 V) from time t13 to time t18, and the negative potential (?5 V) from time t18 to time t25. That is, the first electrode 121 is applied with the AC signal that varies its potential between the positive potential (+5 V) and the negative potential (?5 V), taking the COM potential as a reference, in the second period longer than the first period of the COM signal. Furthermore, in a duration of double periods of the AC signal, the duration in which the first electrode 121 has a positive potential and the duration in which the first electrode 121 has a negative duration have the same length. That is, bias in the polarity of the potential of the first electrode 121 when the AC signal is applied is resolved. Note that, when the number of the electrodes configured for ion trapping is three, an integer multiple (n times) of 6 suffices as the period of the driving signal S1. Furthermore, the second electrode 122 and the third electrode 123 of the peripheral electrode 120 are applied with AC signals having mutually different phases shifted by ? period from that of the AC signal applied to the first electrode 121.
