PROBLEM TO BE SOLVED: To estimate a life of a parallel-connected vacuum tube, prevent the unplanned shutdown of a device by the deterioration of the vacuum tube beforehand in comparison with before, and thereby improve an operating rate of the device and use the vacuum tube to limitation effectively.SOLUTION: A high-frequency power supply device includes: a voltage calculation unit 12a for calculating an average value Vkof cathode voltage Vk of parallel-connected whole vacuum tubes 3 and a voltage change rate Vk' of each vacuum tube 3； a current calculation unit 12b for calculating an average value Igof a grid current Ig of the parallel-connected whole vacuum tubes 3 and a current change rate Ig' of each vacuum tube 3； and a comparing unit 13 for comparing the voltage change rate Vk' with a voltage lifetime setting value Vkand comparing the current change rate Ig' with a current lifetime setting value Ig, and determining that the vacuum tube 3 reaches the end of its lifetime when a determination is made that the voltage change rate Vk' is not more than the voltage lifetime setting value Vkand the current change rate Ig' is not more than the current lifetime setting value Ig.SELECTED DRAWING: Figure 2【課題】並列接続された真空管の寿命を予測して、従来に比べて真空管の劣化による装置の計画外停止を未然に抑制し、装置の稼働率を向上させることと、真空管を限界まで有効に使用する。【解決手段】並列接続された全真空管３のカソード電圧Ｖｋの平均値Ｖｋａｖｅと各真空管３の電圧変化率Ｖｋ’を演算する電圧演算部１２ａ、並列接続された全真空管３のグリッド電流Ｉｇの平均値Ｉｇａｖｅと各真空管３の電流変化率Ｉｇ’を演算する電流演算部１２ｂ、電圧変化率Ｖｋ’を電圧寿命設定値Ｖｋｓと比較するとともに、電流変化率Ｉｇ’を電流寿命設定値Ｉｇｓと比較し、電圧変化率Ｖｋ’が電圧寿命設定値Ｖｋｓ以下、且つ電流変化率Ｉｇ’が電流寿命設定値Ｉｇｓ以下と判定されたときは該当する真空管３が寿命を迎えたと判定する比較部１３、を備えた。【選択図】 図２
