Method of manufacturing a substrate processing apparatus, a substrate manufacturing method and a semiconductor device

To provide a substrate processing apparatus capable of performing accurate temperature control of the reaction tube. The substrate processing apparatus, a reaction tube of processing a substrate (42), a heater for heating the substrate in the reaction tube (42) (46), to flow reaction tube (42) for air cooling to the outside (70) Cooling with use air flow path (72), the reaction tube (42) a thermocouple for detecting the temperature around the (82). Thermocouple (82) is provided in the protective tube cooling air flow path for circulating the cooling air (70) in the state where covered by (86) (72) inside, to the outside of the protective tube (86) is an air cooling a cover member that blocks the flow towards the protective tube (86) (70) (88) is provided.