Substrate Processing Apparatus and Reaction Tube

According to one aspect of the technique, there is provided a substrate processing apparatus including: a substrate retainer supporting substrates; a reaction tube accommodating the substrate retainer, including: a ceiling closing an upper end thereof; and an opening provided at a lower end thereof; a heater provided around the reaction tube and heating an inside of the reaction tube; a gas supplier supplying a process gas to the substrates; a gas discharger communicating with the inside of the reaction tube and exhausting an inner atmosphere of the reaction tube; and a break filter provided in middle of a gas flow path from the gas supplier to the gas discharger in the reaction tube, disposed more downstream than the substrates along the gas flow path and configured to receive heat from an exhaust gas, wherein an inert gas is supplied into the reaction tube through the break filter.