A drying device for a washing machine, performing a drying mode when a washing mode ends, the washing machine including a rotatable drum configured to house laundry items therein, a tub having the drum therein and a driving unit on the tub, connected to the drum and configured to drive the drum, wherein the drying device comprises: a drying unit configured to store liquid water and circulate air in the drum to remove moisture from the laundry when a water level of liquid water reaches a preset water level; and a control unit configured to control operations of the drying unit and adjust the water level of liquid water such that the water level reaches the preset water level, wherein the drying unit comprises: a storage duct under the tub, configured to communicate with the tub and store the liquid water which removes moisture in air while the air passes through the storage duct, a circulation duct connected to the storage duct and configured to supply the air discharged from the tub through openings into the storage duct to the drum, an air blower on the circulation duct and configured to move the air, a heater on the circulation duct and configured to heat the air, and a supply part connected to the circulation duct, configured to supply the liquid water to the storage duct, wherein the storage duct comprises a water level sensor configured to sense the water level of the liquid water, wherein the control unit compares the water level sensed by the water level sensor to the preset water level and adjusts the water level of the liquid water in the storage duct until the water level is at the preset water level, and wherein the drying unit stores water remaining after a rinsing process, water discharged from laundry items during a spin-drying process, or water supplied by the supply part, as the liquid water, characterized in that the storage duct communicates with the tub through a plurality of through-holes and is positioned along the tub length and parallel to a rotational axis of the drum. a drying unit configured to store liquid water and circulate air in the drum to remove moisture from the laundry when a water level of liquid water reaches a preset water level; and a control unit configured to control operations of the drying unit and adjust the water level of liquid water such that the water level reaches the preset water level, wherein the drying unit comprises: a storage duct under the tub, configured to communicate with the tub and store the liquid water which removes moisture in air while the air passes through the storage duct, a circulation duct connected to the storage duct and configured to supply the air discharged from the tub through openings into the storage duct to the drum, an air blower on the circulation duct and configured to move the air, a heater on the circulation duct and configured to heat the air, and a supply part connected to the circulation duct, configured to supply the liquid water to the storage duct, wherein the storage duct comprises a water level sensor configured to sense the water level of the liquid water, wherein the control unit compares the water level sensed by the water level sensor to the preset water level and adjusts the water level of the liquid water in the storage duct until the water level is at the preset water level, and wherein the drying unit stores water remaining after a rinsing process, water discharged from laundry items during a spin-drying process, or water supplied by the supply part, as the liquid water, characterized in that the storage duct communicates with the tub through a plurality of through-holes and is positioned along the tub length and parallel to a rotational axis of the drum.