A method of mounting a substrate support in a chamber includes placing an auxiliary transfer tool having a first portion and a second portion in a chamber which provides a processing space and an additional space, and which has an opening for communication between the additional space and the outside, the first portion in an expanded state being positioned in the processing space and the second portion being positioned in the additional space, inserting a substrate support having a contact portion for supporting the substrate, a rod portion, and a threaded portion connecting to the rod portion, the rod portion being slid on a side surface of the second portion, shrinking the first portion so that the rod portion is moved downward in the additional space and the threaded portion projects out of the chamber through the opening.