A substrate treatment apparatus for treating a substrate, the substrate treatment apparatus includes: an apparatus main body configured to perform a predetermined treatment on the substrate; a casing configured to house a predetermined component therein and to be attachable to and detachable from an upper part of the apparatus main body; a casing side connection part provided at the casing and connected to the predetermined component; a main body side connection part provided at the upper part of the apparatus main body and configured to be fitted into the casing side connection part; a guide part provided at the upper part of the apparatus main body and configured to move the casing in one direction; and a connection assisting mechanism configured to fit the casing side connection part into the main body side connection part while moving the casing in the one direction.