A mass spectrometry device includes an ion source for ionizing a sample, an ion trap for trapping ions ionized by the ion source. A control unit for controlling voltages applied to lenses forming part of the ion trap, and a detection unit for detecting the ions trapped by said ion trap. The control unit causes a trap potential to be generated on a central axis of quadrupole rods forming part of the ion trap, causes part of the trapped ions to be oscillated in an intermediate direction between the quadrupole rods which are mutually adjacent to each other, and applies a voltage for ejecting the oscillated ions in a central-axis direction of the quadrupole rods by generating an extraction field.