Abstract: Disclosed is an apparatus of processing a substrate, the apparatus including: a liquid treating chamber for processing a substrate with a treatment liquid; a recovery tank for recovering the treatment liquid used in the liquid treating chamber through a recovery pipe; and a supply pipe for supplying the treatment liquid recovered from the recovery tank to the liquid treating chamber, in which the recovery tank includes: a tank body having a storage space in which the used treatment liquid is stored; a decompression pipe connected to the storage space and having an opening/closing valve installed; and a decompressor connected to the decompression pipe to decompress the storage space.

Abstract: Disclosed is a liquid exchange method in a liquid supply apparatus. The liquid exchange method in a liquid supply apparatus including a recovery tank, a sub-tank, a main tank, and a pre-tank includes: (a) a liquid exchange operation of the main tank and the sub tank; (b) a flushing operation of the recovery tank; and (c) a liquid exchange operation of the pre-tank, in which in the operation (a), a liquid supply is switched to a double tank operation mode in which a liquid is supplied to a substrate processing apparatus using only the recovery tank and the pre-tank as the pre-tank is switched to a main supply tank.