To prevent leaking of rain to downstairs by positively gathering rainwater on a floor plate into a rain gutter.

A balcony has an end plate 3 extended from the side wall 2 of a building in parallel to the edge of an eaves, a front beam 4 to connect the ends of the end plate 3 and floor plates 9 placed in an area encircled by the front beam 4, the end plate 3 and the side wall 2. On the floor plate 9, a water gradient is applied, which has the upper face sloped down to the edge of the eaves. In this case, the side edges of the floor plates 9 are directed almost in parallel to the end plate 3 to connect each other neighboring floor plates 9 with a first step engaged with a second step and place the floor plates 9 in the condition that the ends on the edge of the eaves side of the floor plates 9 are located from a water inflow port 25 in the front beam 4 into a drain space 26.