Described herein is a technique capable of reducing the time necessary for stabilizing the inner temperature of the processing furnace. A substrate processing apparatus may include: a wafer retainer configured to support a plurality of wafers; an upright cylindrical process vessel; a seal cap configured to cover an opening at a lower end of the process vessel; a first heater configured to heat an inside of the process vessel from a lateral side thereof; an insulating unit disposed between the seal cap and the wafer retainer; and a second heater facing at least one of the plurality of wafers and configured to heat the at least one of the plurality of wafers, the second heater including: a pillar penetrating centers of the seal cap and the insulating unit; an annular member connected to and concentric with the pillar; a pair of connecting parts connecting end portions of the annular member to the pillar; and a heating element disposed inside the annular member.