A
mass spectrometer using a linear
ion trap capable of efficiently suppressing the
space charge and enabling scanning for a wide m / z range at a high
Duty Cycle is provided. The
mass spectrometer comprises: an
ion source for ionizing a specimen to generate ions, an
ion transport portion for transporting the ions, a linear
ion trap portion for accumulating the transported ions by a potential formed axially, and a control portion of ejecting the ions within a second m / z range different from a first m / z range from the linear
ion trap portion substantially at the same timing as the timing of accumulating the ions within the first m / z range to the linear
ion trap portion, in which the control portion conducts control of ejecting the ions
mass selectively from the linear ion trap portion by any of
voltage application of (1) applying a supplemental AC
voltage between at least a pair of linear ion trap rods constituting the linear ion trap portion, (2) applying a supplemental AC
voltage to an end lens constituting the linear ion trap portion, and (3) applying a supplemental AC voltage between inserted lenses, the inserted lenses constituting the linear ion trap portion. The
ion transportation portion having a mass selection means for selecting the ions in the first m / z range.