A base assembly includes a base, a sliding element disposed on the base, a supporting leg pivotably connected to the sliding element, and a supporting leg retractable structure. The sliding element is telescopically slidable to extend and retract with respect to the base. The supporting leg is configured to extend and retract along with the sliding element. The supporting leg retractable structure includes a driving element and a guide assembly. The driving element has an outer circumferential surface formed at least partially into an arc shape. The driving element is configured to pivot together with the supporting leg. The guide assembly is configured to convert a pivoting movement of the outer circumferential surface of the driving element into an actuating force that moves the sliding element and the supporting leg together toward an inside of the base.