A dechuck control method includes performing a discharge process by introducing an inert gas into a processing chamber and maintaining the pressure within the processing chamber at a first pressure; monitoring the pressure of a heat transmitting gas supplied to the processing object rear face and/or the leakage flow rate of the heat transmitting gas; obtaining the amount and polarity of the residual electric charge of the electrostatic chuck surface and applying a voltage for supplying an electric charge that is of the same amount as the residual electric charge but of the opposite polarity to a chuck electrode; evacuating the inert gas from the processing chamber while applying the voltage to the chuck electrode and reducing the pressure within the processing chamber to a second pressure; and turning off the voltage applied to the electrostatic chuck and dechucking the processing object from the electrostatic chuck.