A quadrupole mass spectrometer including a quadrupole mass filter having four pre-rod electrodes (41, 42, 43, 44) provided anterior to four main rod electrodes (31, 32, 33, 34) for selectively allowing a passage of an ion originating from a sample according to a mass-to-charge ratio of the ion, comprising: a) a quadrupole driver including a direct-current voltage source (62, 63) for generating a direct-current voltage whose voltage value changes according to the mass-to-charge ratio of a measurement target, a radio-frequency voltage source (61, 64) for generating a radio-frequency voltage whose amplitude changes according to the mass-to-charge ratio of the measurement target, and a voltage adder for applying, to the main rod electrodes (31, 32, 33, 34), a voltage produced by adding the direct-current voltage and the radio-frequency voltage; and b) a transient voltage supplier (65, 66) for generating, when both the radio-frequency voltage and the direct-current voltage are simultaneously changed so as to switch the mass-to-charge ratio of the measurement target, a voltage corresponding to a transient state of the change of the direct-current voltage and for applying this voltage to the pre-rod electrodes (41, 42, 43, 44); characterized in that a response time t of the direct-current voltage is set to be shorter than a period of time required for an ion having a highest mass-to-charge ratio among a target of analysis to pass through the main rod electrodes (31, 32, 33, 34); a response time t of the amplitude of the radio-frequency voltage is set to be shorter than the response time t of the direct-current voltage when both the radio-frequency voltage and the direct-current voltage are simultaneously changed so as to switch the mass-to-charge ratio of the measurement target; the transient voltage supplier (65, 66) outputs a voltage, which is higher for a greater temporal change in a direct-current voltage and decreases as the temporal change becomes slower, and is configured for generating the voltage corresponding to the transient state of the change of the direct-current voltage and for applying this voltage to the pre-rod electrodes (41, 42, 43, 44) so as to block an ion of a low mass-to-charge ratio that can pass through the main rod electrodes (31, 32, 33, 34) due to a difference in the response time between the radio-frequency voltage and the direct-current voltage while these voltages are being changed; the transient voltage supplier (65, 66, 68, 69) is a differentiation circuit; and a time constant of the differentiation circuit (65, 66, 68, 69) is set to be greater than one third of a response time t of the direct-current voltage generated by the direct-current voltage source (62, 63). a) a quadrupole driver including a direct-current voltage source (62, 63) for generating a direct-current voltage whose voltage value changes according to the mass-to-charge ratio of a measurement target, a radio-frequency voltage source (61, 64) for generating a radio-frequency voltage whose amplitude changes according to the mass-to-charge ratio of the measurement target, and a voltage adder for applying, to the main rod electrodes (31, 32, 33, 34), a voltage produced by adding the direct-current voltage and the radio-frequency voltage; and b) a transient voltage supplier (65, 66) for generating, when both the radio-frequency voltage and the direct-current voltage are simultaneously changed so as to switch the mass-to-charge ratio of the measurement target, a voltage corresponding to a transient state of the change of the direct-current voltage and for applying this voltage to the pre-rod electrodes (41, 42, 43, 44);