PURPOSE:To improve the reliability of beam guide-out windows by synchronizing the current of a coil for scanning with pulses of an electron beam and providing plural beam guide-out windows which are made small. CONSTITUTION:Electron beams which are accelerated by an accelerating tube 2 pass, for example, only four beam lines 15a, 15b, 15c, and 15d when current which are synchronized with pulses of the electron beams are supplied to coils 4a and 4b for scanning. On those four beam lines, the small beam guide-out windows 11a, 11b, 11c, and 11d are provided and beam currents which are equal to one another can be led out of the four beam guide-out windows; and no beam enters a vacuum duct for scanning except those beam guide-out windows 11a - 11d.
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