An electrode changeover switch which switches the connection state of electrodes is provided in the wiring path between eight electrodes through, arranged rotation-symmetrically about ion optical axis, and voltage generation switch which generates square wave high voltage ±V. When switch is switched as shown in the drawing, two circumferentially adjacent rod electrodes are connected to form one set, a square wave voltage of opposite phase is applied to circumferentially adjacent sets, and an effectively quadrupole electric field is formed. When switch is switched, a square wave voltage of opposite phase is applied to circumferentially adjacent rod electrodes and an octupole electric field is formed. In this way, by switching the switch according to the mass range, etc., it becomes possible to rapidly switch the number of poles of a multipole electric field and to suitably transport ions.