PURPOSE: To allow a door to be closed airtightly without providing a sill or the like with step difference by forming a door closing device of a casing fitted along the lower edge of the door, an operating rod, arms and a seal member.

CONSTITUTION: An operating rod 2 is slidably supported in a casing 1, a long- sized member fitted along the lower edge of a door, and the pressing part 3 of the operating rod 2 in the protruding state from the side face of the door is retreated being pushed by a door frame by the closing of the door. The variable length part 4 of the operating rod 2 is then compressed, and a support pin 7 is advanced downward by two arms 5, 6 so as to press a seal member 10 to a sill or the floor face. The door can thereby be closed airtightly without providing the sill or the like with step difference.