An apparatus for treating a substrate includes a chamber having a treatment space in which the substrate is treated, a substrate support unit that supports the substrate in the treatment space, a gas supply unit that supplies a gas into the treatment space, an exhaust line connected to the chamber, and a pressure-reducing member that reduces pressure in the exhaust line and releases process by-products generated in the treatment space. The exhaust line includes a first line connected to the chamber, a second line equipped with the pressure-reducing member, and a filter tube that connects the first line and the second line, and the filter tube has a corrugated side surface.