A mass spectrometer according to the present invention has an ionization source for generating ions; an ion trap for accumulating the ions; a time-of-flight mass spectrometer for performing mass spectrometry analysis on the ions by use of a flight time; a collision damping chamber disposed between the ion trap and the time-of-flight mass spectrometer and having a plurality of electrodes therein, which produce a multi-pole electric field, wherein a gas is introduced into the collision damping chamber to reduce kinetic energy of the ions ejected from the ion trap; and an ion transmission adjusting mechanism disposed between the ion trap and the collision damping chamber to allow or prevent injection of the ions from the ion trap to the collision damping chamber. The mass spectrometer provides greatly enhanced qualitative and quantitative analysis capabilities, as compared with conventional techniques.