Abstract: Proposed is an automatic liquid drain device including a body (10) having a water collection chamber (12) and configured such that an upper cap member (11) having a liquid inlet (13) is fastened to an upper portion of the water collection chamber (12), a buoyancy valve member (20) embedded to be vertically movable in the water collection chamber (12), having downward-inclined ribs (23) and a drop drain (24), and provided with a valve packing (25) protruding from a lower center thereof, a liquid pooling space (122) below the buoyancy valve member (20), and a drain emergency action means (30) provided with a drain nipple (31) having a vertical drain hole (32) whose upper end is exposed to the liquid pooling space (122), and an opening/closing nipple (34) fastened to a lower portion of the drain nipple (31) to open and close the vertical drain hole (32).