PURPOSE: To enable one constant current circuit to control plural circuits stably and simultaneously, by connecting a power controller is series to a focusing coil for an electromagnetic focusing type image pickup tube and driving this series circuit by a constant current.

CONSTITUTION: In a figure, 10 is the focusing coil designed to provide focusing to an optimum value (rated current value) of a current flowing through a heater circuit 11, 12 is a constant current circuit, and 9 is a chopper power source. The heater circuit 11 and focusing oil 10 are connected to the constant current circuit 12 in series and controlled. It is easy to design the focusing coil 10 so that focusing is carried out the rated current value of the current flowing through the heater circuit 11, and the heater circuit 11 and focusing coil 10 are controlled simultaneously by the constant current circuit 12; and a dummy resistance connected conventionally to the heater circuit 11 in series, or a constant voltage circuit which is stabilized with a heater voltage value is unnecessary, so electric power loss is reduced to improve the efficiency.