A wafer processing apparatus includes a reaction tube extending in a vertical direction, a door plate configured to load a boat into the reaction tube and positioned under the reaction tube to seal the reaction tube, the boat supporting a plurality of wafers thereon, a gas injector extending in the vertical direction along the boat within the reaction tube and including a plurality of ejection holes formed therein, a rotary mechanism configured to rotate the gas injector about its center axis to adjust an angle of the ejection hole toward the wafer, and a lift mechanism configured to move the gas injector upward and downward to adjust a height of the ejection hole on the wafer.