A connection control method in a substrate processing apparatus is provided. The substrate processing apparatus comprises: a depressurized processing room; a susceptor that is provided in the processing room and configured to mount a wafer thereon; a HF high frequency power supply configured to apply a high frequency voltage for plasma generation to the susceptor; a LF high frequency power supply configured to apply a high frequency voltage for a bias voltage generation to the susceptor; and a DC voltage applying unit configured to apply a DC voltage of a rectangle-shaped wave to the susceptor, capable of improving a processing controllability in an etching process. The connection control method comprises controlling connection or disconnection between the susceptor and the LF high frequency power supply and connection or disconnection between the susceptor and the DC voltage applying unit when plasma is generated in the processing room.