Disclosed is an apparatus for treating a substrate. The apparatus includes: an RF power supply; a process chamber which performs plasma processing by using power applied from the RF power supply; and an impedance matching unit which is disposed between the RF power supply and the process chamber and performs matching, in which the RF power supply includes a first sensor measuring impedance in a direction of the process chamber and the impedance matching unit, and the impedance matching unit performs impedance matching by reflecting impedance measured in the RF power supply through the first sensor.