Abstract: A substrate treating apparatus includes a chamber having a treatment space in the interior thereof, a support unit that supports a substrate in the treatment space, a gas supply unit configured to supply a treatment gas into the treatment space, and a plasma source configured to generate plasma from the treatment gas. The support unit includes an electrostatic chuck, on which the substrate is positioned, a first ring surrounding a circumference of the substrate positioned on the electrostatic chuck, a second ring surrounding a circumference of the electrostatic chuck and formed of an insulation material, an insertion body disposed in the second ring and formed of a conductive material, and an impedance control unit configured to adjust an impedance of the insertion body.