PURPOSE: To suppress damage of a traveling wave tube to possible minimum even in the event of abnormality occurrence or malfunction and keep an eventually damaged circuitry at a degree which ensures at least communications by sinking the anode voltage of the traveling wave tube, in case any abnormality has occurred in a source power supply, in conformity to a signal as sensing the abnormality once to the voltage at which the high frequency output power becomes a specific dB, and then restituting the anode voltage.

CONSTITUTION: A power supply 12 for a traveling wave tube is composed of a rectifier circuit 13, sensing circuit part 14 for abnormality occurrence, anode voltage control part 15, filament power supply 16, anode power supply 17, helix power supply 18, and collector power supply 19. The power suplies are connected with respective specified parts of the traveling wave tube. During service, eventually generated abnormality in the source power supply is sensed, and the anode voltage specified for the b]1b concerned is sunk once to the voltage at which the high frequency output power becomes approx. -3dB (approx. 90%), provided that the anode voltage and helix voltage are not completely shut off.