Provided is a quadrupole mass spectrometer including direct-current voltage sources having response characteristics which ensure that the response time of the direct-current voltage will be shorter than the period of time required for an ion having the highest mass-to-charge ratio (m/z) among the ions introduced into a quadrupole mass filter to pass through this filter. Main rod electrodes and pre-rod electrodes are connected to each other via primary differentiation circuits. Thus, in the transient state of the voltage change due to the switching of the mass-to-charge ratio, among the ions entering the quadrupole mass filter, ions having low m/z values can be removed by a pre-electrode unit, and ions having high m/z values can be removed by a main electrode unit. Accordingly, a large amount of ions can be prevented from passing through the filter and entering an ion detector.