A substrate-treating apparatus includes: a plurality of modules disposed along a first direction, each of the plurality of modules having an inner space for containing a substrate; a transfer unit transferring the substrate among the plurality of modules, the transfer unit including at least one track disposed along the first direction and at least one movable transfer chamber moving along the at least one track; and a gate valve fixed to each of the plurality of modules and combined with the at least one movable transfer chamber. The at least one movable transfer chamber is isolated from an exterior atmosphere while moving.