Substrate Processing Apparatus and Gas Box

Described herein is a technique capable of preventing a deterioration in controllability of a gas flow rate in a substrate processing apparatus. According to one aspect thereof a substrate processing apparatus includes: a process furnace including a process chamber; a process gas supply path; a process gas supply controller; a heater configured to heat at least a part of the process gas supply controller or the process gas supply path; a gas box accommodating the process gas supply path, the process gas supply controller and the heater. The gas box includes: an inlet port configured to introduce an outer atmosphere; an exhaust port connected to an exhaust duct and configured to exhaust an inner atmosphere to the exhaust duct; a temperature controller configured to lower and monitor a temperature of the inner atmosphere; and a gas leakage sensor configured to detect the process gas leaked in the gas box.