A time-of-flight mass spectrometer in which a predetermined energy is given to ions to make the ions fly in a flight space to temporally separate the ions in accordance with their mass and detect the ions with an ion detector, the mass spectrometer comprising: a plurality of first ion optical systems and at least one second ion optical system, in each of said plurality of first ion optical systems an ion inlet, an ion outlet, and a flight orbit being provided on a plane (P1, P2, P3), the flight orbit being formed by electric fields including a plurality of sector-shaped electric fields formed by four pairs of toroidal sector-shaped electrodes (11, 12, 13, 14) and being so that ions injected from the ion inlet satisfy a time-focusing condition at the ion outlet, in each of said first ion optical systems a direction of an injection of an ion at the ion inlet and a direction of an ejection of an ion at the ion outlet being the same, in said at least one second ion optical system an ion inlet, an ion outlet, and a flight orbit being provided, the flight orbit being formed by electric fields including a plurality of sector-shaped electric fields formed by three pairs of toroidal sector-shaped electrodes (21, 22, 23, 24, 25, 26) and being so that ions injected from the ion inlet satisfy a time-focusing condition at the ion outlet, in said at least one second ion optical system a direction of an injection of an ion at the ion inlet and a direction of an ejection of an ion at the ion outlet being opposite, wherein adjacent first ion optical systems are tandemly connected through a corresponding second ion optical system in such a manner that the ion outlet of one adjacent first ion optical system is connected to an ion inlet of a subsequent adjacent first ion optical system through said corresponding second ion optical system, and wherein the plurality of first ion optical systems are placed on mutually-different planes (P1, P2, P3) in such a manner that the planes (P1, P2, P3) are parallel to each other and mutually separated in a direction orthogonal or oblique to the planes (P1, P2, P3). a plurality of first ion optical systems and at least one second ion optical system, in each of said plurality of first ion optical systems an ion inlet, an ion outlet, and a flight orbit being provided on a plane (P1, P2, P3), the flight orbit being formed by electric fields including a plurality of sector-shaped electric fields formed by four pairs of toroidal sector-shaped electrodes (11, 12, 13, 14) and being so that ions injected from the ion inlet satisfy a time-focusing condition at the ion outlet, in each of said first ion optical systems a direction of an injection of an ion at the ion inlet and a direction of an ejection of an ion at the ion outlet being the same, in said at least one second ion optical system an ion inlet, an ion outlet, and a flight orbit being provided, the flight orbit being formed by electric fields including a plurality of sector-shaped electric fields formed by three pairs of toroidal sector-shaped electrodes (21, 22, 23, 24, 25, 26) and being so that ions injected from the ion inlet satisfy a time-focusing condition at the ion outlet, in said at least one second ion optical system a direction of an injection of an ion at the ion inlet and a direction of an ejection of an ion at the ion outlet being opposite, wherein adjacent first ion optical systems are tandemly connected through a corresponding second ion optical system in such a manner that the ion outlet of one adjacent first ion optical system is connected to an ion inlet of a subsequent adjacent first ion optical system through said corresponding second ion optical system, and wherein the plurality of first ion optical systems are placed on mutually-different planes (P1, P2, P3) in such a manner that the planes (P1, P2, P3) are parallel to each other and mutually separated in a direction orthogonal or oblique to the planes (P1, P2, P3).