To provide a plant cultivation unit for greening a rooftop and surroundings of a building, making it possible to green the rooftop in accordance with strength of the building, not requiring a waterproof base material, etc., capable of being changed in planting design, capable of being easily subjected to cultivation management, and having high earthquake- resisting and wind-resisting functions.

In this plant cultivation unit, a cultivation tank 1 has structures 2 for moving the tank, metal fittings 3 for fastening the tank to the building, a waste pipe 4 which is positioned outside the tank and of which the terminal has a connector 16 capable of being joined to an adjacent cultivation tank for liquid drainage, a waste liquid outlet 6 which is joined to the waste pipe and has a filter 5, a liquid supply pipe 7 of which the terminal has another connector capable of being joined to the adjacent cultivation tank for fluid supply, a structure 8 for preventing the plant from falling, etc. Further, the cultivation tank is filled with a planting base material, such as a soil, and further with a water-permeable material 10 laid under the planting base material as a lower layer. When moisture contained in the planting base material is sensed by a soil moisture sensor 11, a signal is transmitted to a controller 13 equipped with a timer 12, so that the controller operates a power supply unit 14, drives a liquid supply unit 15 by electric power given by the power supply unit, and supplies a culture liquid to the tank. Thus, the plant for greening the rooftop and the surroundings of the building is cultivated in the plant cultivation unit.