PURPOSE: To simplify the operation of an electron-gun power source remarkably by heating the filament part of an electron gun gradually to a high temperature, and continuing heating the filament part at an appropriate temperature after the filament part reaches close to a stable condition.

CONSTITUTION: An electron-gun power source consists of an accelerating power source 2 used for applying high voltage for accelerating electrons discharged from the filament part across a filament cathode (K) and an anode (A) of an electron gun 1, a heating power source 3 used for supplying a heating current to the filament part, an accelerating-power-source control circuit 4 which controls the power sources 2 and 3 and consists of an accelerating standard-voltage source (VR1), a switch (S1) and a gate transistor (TR1), and a heating-power- source control circuit 5 which consists of a heating standard-voltage source (VR2), a switch (S2), a functional-voltage generating circuit (FU) generating voltage signals being a primary function of time, a (TR2) and a diode (D). As the result, operation of the electron-gun power source becomes extremely simple, and even a beginner can operate it easily.