In a plant cultivation apparatus where plants are cultivated in a culture medium of a planter (4), viruses, bacteria, and insects can grow when leaves of the plants fall over the medium, and the leaves cover the upper portion of the medium block the air from getting through the medium. In the present invention, the planter (4) has an upper drain pipe (7,10) and a lower drain pipe (5), and nutrient solutions are supplied over the medium. When the nutrient solutions are supplied, a sufficient amount is supplied to be overflowing over the medium while the nutrient solutions are passing through the lower drain pipe (5). The overflowed nutrient solutions drag impurities out of the medium to discharge the impurities through the upper drain pipe (7,10) and the discharged impurities are filtered by a filter (9) between the upper drain pipe (7,10) and a nutrient solution tank (1). Even if the entry of the lower drain pipe (5) is located at the lower portion of the planter (4), the pipe is curved in the upward and downward direction so that the nutrient solutions staying in the bottom of the planter (4) are discharged when the nutrient solutions begin passing through, in accordance with the siphon principle. In the process, the nutrient solutions filling the voids in the medium are discharged and air is sucked in through the voids by a pressure difference so that the sufficient oxygen is supplied to the roots of the plants. The accumulation of the salts on the upper portion of the medium is prevented as the upper portion of the medium is filled by the nutrient solutions.플랜터(4)에 배지를 담아서 식물을 재배하는 양액재배기에 있어서, 식물의 잎이 배지 위로 떨어지면 바이러스, 세균, 벌레 등이 자라고, 배지 위를 덮은 식물의 잎은 배지 내로 공기가 들어가는 것을 막게 된다. 본 발명은 플랜터(4)에 상부배수관(7,10)과 하부배수관(5)을 두고, 양액은 배지 위로 공급한다. 양액을 공급할 때 양액의 양이 충분하여 하부배수관(5)으로 양액이 빠져 나가는 상태에서도 배지 위로 양액이 범람하도록 한다. 범람한 양액은 배지의 불순물을 끌어내어 상부배수관(7,10)으로 배출하고, 상부배수관(7,10)과 양액탱크(1) 사이에 있는 필터(9)에서 불순물을 걸러낸다. 하부배수관(5)의 입구는 플랜터(4)의 하부에 위치해 있지만 관이 위로 올랐다가 내려가는 구조로 되어 있어 사이펀의 원리에 의해 양액이 빠져나가
