A plasma processing apparatus 100 is equipped with a shower head 16 and a placing table 2 facing each other. A first RF power supply 10a is configured to apply a RF power to any one of the shower head 16 or the placing table 2 without igniting plasma. A measuring device 204 is configured to measure a physical quantity of the RF power applied by the first RF power supply 10a. A process controller 91 is configured to acquire an inter-electrode distance by using the measured physical quantity of the RF power in a correlation function of the inter-electrode distance and the physical quantity of the RF power.