According to one aspect of the technique described herein, there is provided a technique including: a reaction tube defining a processing chamber wherein a substrate is processed; an electrode provided at an outer circumferential surface of the reaction tube and configured to generate plasma in the process chamber; an electrode fixing part configured to fix the electrode thereto; a heater provided at an outer circumferential surface of the electrode fixing part and configured to heat an inside of the reaction tube; and a spacer configured to provide a predetermined gap between the electrode and a surface of the electrode fixing part.