Embodiments of the inventive concept provide an apparatus and method for storing a substrate. A buffer unit for storing a substrate includes a housing having an entrance formed at one side and a buffer space inside, a substrate support unit that supports one or more substrates in the buffer space, a pressure adjustment unit that adjusts pressure in the buffer space, and a controller that controls the pressure adjustment unit. The pressure adjustment unit includes a gas supply line that supplies a gas for pressurizing the buffer space and a gas exhaust line that reduces the pressure in the buffer space. At least one of the gas supply line and the gas exhaust line includes a plurality of lines.