PURPOSE: To eliminate the flickers of a fluorescent character display tube and to control the working of a part to be controlled and the lighting drive of the flourescent character display tube with just a single microcomputer, by providing a power supply circuit having a frequency difference that has no interference with a dynamic lighting drive frequency with a heater of the fluorescent character display tube.

CONSTITUTION: When the DC power supply is supplied to a power supply circuit 12 from a power supply terminal 15, an oscillation output is obtained from an oscillation output is obtained from an oscillation part 13. This output is amplified by an output amplifier circuit 14 and supplied to a heater 6. When a code signal is supplied to an input circuit 2, this signal is read by a microcomputer 11. Then the computer 11 controls a part 3 to be controlled as well as the dynamic lighting drive in order to display the working state of the part 3 to a fluorescent character display tube 5. No flicker is perceived when the difference exceeds ≥35Hz between the dynamic lighting drive frequency of the tube 5 and the oscillation frequency of an oscillation part 13 of the circuit 12 of the heater 6. Therefore the oscillation frequency of the part 13 is set at about 35Hz {dynamic lighting frequency (70Hz) - frequency (35Hz)}.