Abstract: A high-frequency power supply system includes an anomaly detector 3 which detects an anomaly occurring in a circuit on the side of a load L as from an outputting end A of a high-frequency power source 1. The anomaly detector 3 includes a first detector 21 which detects a voltage value Vf of a high-frequency forward wave, a second detector 22 which detects a voltage value Vr of a high-frequency reflected wave, a reflection coefficient calculator 23 and a differentiator 24 which calculate a reflection coefficient differential value d?/dt from the forward wave voltage value Vf and the reflected wave voltage value Vr, and an anomaly determiner 25 which determines of an occurrence of an anomaly based on the reflection coefficient differential value d?/dt. When the anomaly detector 3 outputs an anomaly detection signal to the high-frequency power source 1, high-frequency power source 1 stops its power output operation.