The vacuum tube subject to the present invention comprises a filament and two pairs of a grid and an anode. The filament is tensioned linearly and emitting thermoelectrons. Both of the anodes are formed on the same face on a planar substrate. The filament is arranged parallel to the planar substrate at a position facing both of the anodes. Each of the grids is arranged, such that the grid faces the anode in the same pair at a first predetermined distance from the anode and has a second predetermined distance from the filament, between the anode and the filament. The vacuum tube comprises an intermediate filament fixing part fixing the filament at a position corresponding to an intermediate point between the anodes of the two pairs.