A substrate processing apparatus is provided. The substrate processing apparatus includes: an electro-static chuck configured to retain a substrate on a platform by electrostatic attraction; an ionized gas generation unit configured to ionize a pressure-controlled gas to generate an ionized gas; a gas supplying path, which is made of insulating material or to whose inner surface insulating processing is applied, configured to allow passage of the generated ionized gas; a gas supplying tube configured to supply the ionized gas that has passed the gas supplying path to a gap between the substrate and the electro-static chuck; and a gas exhaust path, which is provided inside the platform, configured to exhaust the gas that has been supplied to the gap.