PURPOSE: To obtain a deflector wherein no false signal is generated, in regard to a helical deflector having a delayed wave structure.

CONSTITUTION: In a helical deflector which is constructed of a core and a deflecting voltage transmission electrode 1 wound round helically on this core and of which the core is constructed of a GND plate 2 and two dielectric support plates 3 disposed in parallel substantially so that they hold this GND plate 2 between them and fitted to the opposite lateral sides of the GND plate 2 respectively, the deflecting voltage transmission electrode 1 is inclined to the GND plate 2. Therefore, electrons do not enter between the deflecting voltage transmission electrode 1 and the GND plate 2 or the path thereof is blocked by the deflecting voltage transmission electrode 1 even when they enter. Accordingly, no false signal is outputted onto an output face.