An object of the present invention is to provide a mass spectrometer and a mass separator whose design and performance are less restricted by problems arising from the principle of operation, and which have in principle no limitation on the mass-to-charge ratio range to be able to deal with and are each capable of repeatedly analyzing or extracting plural ionic species of different mass-to-charge ratios in a short time.A mass spectrometer (10) is configured from an ion source (1), an ion introduction unit (2), a mass analyzer (3), an ion detection unit (4), and the like. Crude ions are introduced into a separation space (5) at a predetermined acceleration voltage as a pulse synchronized with the phase of a one-dimensional high-frequency electric field. In the separation space (5), each ion travels in an incident direction by inertia, and besides they are displaced by force received from the one-dimensional high-frequency electric field which acts in the y-direction crossing the incident direction. Ionic species having different mass-to-charge ratios with each other are separated by the difference in displacement magnitude. At this time, the acceleration voltage and the period of the one-dimensional high-frequency electric field are set in order that the measured ionic species may exit from the separation space (5) having received the action of the electric field for one period.