To provide a method for shortening time required to screen ions by simplifying control and adjustment of an ion screening waveform, in an ion storage device.

An ion screening electric field produced in proportion of the product of an ion screening waveform obtained by repetition of a waveform with a fixed magnitude and a constant pattern and a continuously changing magnitude signal waveform is impressed on the ion storage space of this ion storage device, and thereby ions in a range of a specific mass/charge ratio are screened. The continuously changing magnitude waveform is a wave the magnitude of which increases as time elapses. The ion screening waveform obtained by repetition of the waveform with the fixed pattern is produced by a FNF (Filtered Noise Field) method and a SWIFT (Stored Wave Inverse Fourier Transform) method. In addition, in the waveform with the constant pattern, the strength of a frequency component apart from the frequency by which the ions within the range of the specific mass/charge ratio oscillates is strengthened.