The disclosure provides an assembly method of a vacuum processing apparatus having a reaction vessel and an exhaust port that are made of quartz and airtightly connected to each other, in order to prevent breakage of the vessel. The method includes (a) mounting an attachment member on one end portion of the reaction vessel, (b) connecting and fixing at least a flange portion of an exhaust pipe to the exhaust port, (c) fixing the attachment member to a portion of the exhaust pipe including at least the flange portion connected and fixed to the exhaust port by using fixing members after (a) and (b), (d) fixing the attachment member to a support portion after (a), and (e) fixing the exhaust pipe to an exhaust pipe fixing portion different from the attachment member at a lower position than a fixing position of the attachment member after completing (a) to (d).