A substrate processing apparatus includes a vacuum chamber; a turntable rotatably provided in the vacuum chamber, on which a circular substrate is to be mounted, and provided with a circular concave portion at a front surface having a larger diameter than that of the substrate, and a circular substrate mounting portion provided in the concave portion having a diameter smaller than that of the concave portion and the substrate at a position higher than a bottom portion of the concave portion, the center of the substrate mounting portion being off center with respect to the center of the concave portion toward an outer peripheral portion side of the turntable; a process gas supplying unit which supplies a process gas to the substrate; and a vacuum evacuation mechanism which evacuates the vacuum chamber.