Described herein is a technique capable of reducing an amount of moisture in a low temperature region in a substrate processing apparatus provided with a transfer chamber. According to one aspect of the technique, there is provided a substrate processing apparatus including: a process chamber provided with a heater; a load lock chamber; a transfer chamber provided between the process chamber and the load lock chamber and including a first region provided adjacent to the process chamber and a second region provided more adjacent to the load lock chamber than the first region and whose temperature is lower than a temperature of the first region; a detector capable of detecting an amount of moisture in the transfer chamber; and an inert gas supplier capable of supplying an inert gas toward the second region in the transfer chamber.