In an acceleration tube conditioning apparatus for performing a conditioning process on an acceleration tube when a high frequency power signal to be supplied to an acceleration tube is generated by a high frequency power supply, a power value collecting section collects a traveling wave power value and a reflection wave power value from a sensor which monitors the traveling wave power signal and the reflection wave power signal. A high frequency calculating section calculates a resonance frequency of the acceleration tube based on the traveling wave power value and the reflection wave power value. A high frequency adjusting section determines a high frequency value based on one of the traveling wave power value and the reflection wave power value as a selection power value, and a high frequency power supply control unit controls the high frequency power supply based on the high frequency value. The high frequency value indicates a constant value when the selection power value is smaller than a predetermined value, and indicates the calculated resonance frequency when the selection power value is larger than the predetermined value.