Apparatus for processing substrate for supplying reaction gas having phase difference

Provided is a substrate processing apparatus. The substrate processing apparatus in which processes with respect to substrates are performed includes a lower chamber having an opened upper side, the lower chamber including a passage allowing the substrates to pass therethrough in a side thereof, an external reaction tube closing the opened upper side of the lower chamber to provide a process space in which the processes are performed, a substrate holder on which the one ore more substrates are vertically stacked, the substrate holder being movable between a stacking position in which the substrates are stacked within the substrate holder and a process position in which the processes with respect to the substrates are performed, and a gas supply unit disposed inside the external reaction tube to supply a reaction gas into the process space, the gas supply unit forming a flow of the reaction gas having different phase differences in a vertical direction.