A substrate processing apparatus comprises a substrate transfer chamber; a plurality of substrate processing chambers disposed on a first side wall of the substrate transfer chamber and stacked in the vertical direction; a plurality of first gate valves, each being disposed between each of the substrate processing chambers and the substrate transfer chamber; a substrate accommodating chamber disposed on a second side wall of the substrate transfer chamber; a substrate transfer device, disposed within the substrate transfer chamber, for transferring the substrate under reduced pressure between the substrate processing chambers and the substrate accommodating chamber; an elevator disposed outside the substrate transfer chamber and comprising a stationary portion and an elevating portion which is vertically movable with respect to the stationary portion; a rigid connecting member capable of moving through a through-hole formed in a predetermined face of the substrate transfer chamber, the rigid connecting member mechanically connecting the elevating portion and the substrate transfer device through the through-hole; and a sealing member for establishing a hermetic vacuum seal between the predetermined surface and the connecting member which penetrates through the through-hole.
