Abstract: A quadrupole mass spectrometer includes a quadrupole mass filter including: a main rod portion including four main rod electrodes; a pre-rod portion including four pre-rod electrodes, where, at an end opposite to the main rod portion, the four pre-rod electrodes are disposed to be aligned on an inscribed circle having the same radius centered on the ion optical axis, and, at the other end facing the main rod portion, two pre-rod electrodes facing each other across the ion optical axis and the other two pre-rod electrodes are disposed to be aligned on an inscribed circle having different radii centered on the ion optical axis; a main voltage applying unit to apply, to each main rod electrodes, a voltage created by superimposing a DC voltage and an RF voltage; and a pre-voltage applying unit to apply an RF voltage having a same frequency as the RF voltage to each pre-rod electrodes.