The mass spectrometer is characterized in that a linear ion trap, that consists of electrodes for mass-selective discharge, is provided with a mechanism that excites ions in a first direction that is perpendicular to the rod axes and a mechanism that simultaneously generates an electric field on the axes in a second direction that is perpendicular to the axial direction and the first direction in order to generate an electric field on the central axis. Highly efficient, high-speed scanning can be achieved using this configuration.