A working chamber includes: a body case including a work space； a supply device configured to supply gas in a body case； a work plate having an opening formed therein, the work plate configuring a bottom surface of the work space； and an observation device capable of being lifted and lowered, and the observation device includes a receiving portion having a width greater than a gap between the work plate and the observation device in an in-use state, and the receiving portion is configured to close the gap between the observation device and the work plate in the in-use state.
