PURPOSE: A plasma diagnostic apparatus is provided to calculate electron density and temperature from the current size of a vibration frequency in a bottom electrode by estimating the selection ratio from a DC component of a measured voltage at a detector. CONSTITUTION: A chamber unit(10) comprises an upper electrode(3) and a bottom electrode(6). A plasma generating unit(20) generates plasma inside the chamber unit. A bias supply unit(30) applies a bias to the bottom electrode. A signal supply unit(40) is directly connected to the bottom electrode. An analysis unit(50) analyzes the harmonic components of a current. A capacitor(60) blocks the DC component of a current which is generated in the bottom electrode. A DC detector measures the DC component the current which is generated in the bottom electrode.
