A substrate processing apparatus includes a radio-frequency power supply part configured to supply radio-frequency power for plasma generation to a processing container, and a monitoring part configured to detect an abnormality in the supply of the radio-frequency power to the processing container, wherein the monitoring part is configured to detect the abnormality in the supply of the radio-frequency power to the processing container based on a signal data obtained by sampling a signal propagating between the radio-frequency power supply part and the processing container at a sampling frequency higher than a frequency of the radio-frequency power.