Abstract: Described herein is a technique capable of suppressing or preventing an inside of a source gas nozzle from being heated to a substrate processing temperature when a source gas is supplied through the source gas nozzle into a reaction tube in which a substrate is accommodated. According to one aspect of the technique, there is provided a substrate processing apparatus including: a reaction tube made of a first material and capable of accommodating a substrate; and a source gas nozzle provided in the reaction tube and at least a part thereof made of a second material whose reflectance is higher than that of the first material and whose surface is rougher than that of the first material by bubbles contained therein, wherein a source gas is supplied through the source gas nozzle.