Abstract: A substrate processing apparatus includes a process room for treating one or more substrates, an antechamber of a loadlock type installed to be adjoined to the process room, and a buffer chamber installed to be adjoined to the antechamber, the buffer chamber being maintained at an atmospheric pressure while the one or more substrates are transferred from a carrier for accommodating the one or more substrates to the buffer chamber and at a vacuum condition while the one or more substrates are transferred from the buffer chamber to the antechamber. The buffer chamber is equipped with a loading port for loading the carrier at a top or a side portion thereof. The antechamber is equipped with a stocker for storing one or more product substrates or/and one or more dummy substrates therein. The elevator is arranged at a corner portion of the antechamber in order to reduce dead space.