PURPOSE: To shape a drain strainer which does not cause stumbling on walking.

CONSTITUTION: A drain ditch 21 is formed with a drainage slope on the floor 13 of a balcony on which rain falls and a box type drain strainer 31 formed on the almost same level plane with the floor 13 at the upper end face thereof is contained in a sump 22 of the terminal end in the downstream side of the drain ditch 21. In this way, since the floor 13 is almost the same level with the upper end face of the drain strainer 31, the structure does not cause stumbling when one walks on the floor.