Method of mass spectrometry and mass spectrometer

A mass spectrometry device, comprising:

• an ion source for ionizing a sample,
• an ion trap for trapping ions ionized by said ion source, said ion trap including an inlet end lens, an outlet end lens, quadrupole rods, and a trap lens,
• a control unit for controlling voltages applied to said lenses configuring said ion trap, and
• a detection unit for detecting said ions trapped by said ion trap, wherein
• said control unit causes a trap potential to be generated on central axis of said quadrupole rods,
• causes part of said trapped ions to be oscillated in an intermediate direction between said quadrupole rods which are mutually adjacent to each other, and applies
• a voltage for ejecting said oscillated ions in a central-axis direction of said quadrupole rods by generating an extraction field.