PURPOSE: To reduce the cost by employing single insulated transformer while controlling the grid voltage at high potential by means of an electron beam current controller thereby reducing the size and simplifying.

CONSTITUTION: Each power sources A, B, C, for filament, shock and grid to be connected to the electron beam acceleration voltage are power supplied from three secondary windings of single common insulation transformer 1d. The electron beam current controller 7b is connected to the secondary winding for the grid power source of the transformer 1d thus to peroform the control of the grid voltage under high potential. When employing a common insulation transformer in such a manner, the common insulation level is achieved while the size is reduced and when reducing the required number of the insulated transformer the wiring work is simplified resulting in the reduction of cost.