To provide a building-greening unit and a building-greening apparatus equipped with a sufficient water holding means and a sufficient water supply means.

This building-greening unit is obtained by mounting a supporting container (3) on the top (1a) of an opening in a nearly cylindrical water container (1) having the opened top (1a), enabling roots (7) of plants (5) to pass through at least the bottom (3a) in the supporting container (1), housing coconut fibers (9) on the bottom (3a) in the supporting container (1), housing soil (11) on the coconut fibers (9), setting the soil (11) with the plants (5), introducing a rainwater injecting pipe (13) into the water container (1) and leading out an overflow pipe (15) from a position at a higher level than that of the bottom (3a) of the supporting container (3) in the water container (1) and housing a root rot preventing agent (17) in the water container (1).