An apparatus for cultivating plants, the apparatus comprising: a cabinet having a cultivating space thereinside; a door to open or close the cultivating space; at least one bed provided in the cultivating space and used to cultivate the plants; a light assembly to irradiate the bed with light for photosynthesis; a machine compartment provided at a lower portion of the cabinet, separated from the cultivating space and disposed to receive a compressor and a condenser which form a cooling cycle to control a temperature of the cultivating space; a step part protruding inward of the cultivating space from a position corresponding to the machine compartment; a water supply case disposed in front of the step part; and a water tank to store water to be supplied to the at least one bed, wherein the water tank is provided inside the cultivating space spaced apart from the machine compartment and in front of the water supply case, wherein the water tank is received inside a space defined by the door, the step part, the at least one bed, and a floor of the cultivating space, characterized in that the apparatus further comprises: tank rails disposed at opposite sides of the water tank and coupled to the water tank to withdraw or introduce the water tank; a suction pipe provided inside the water tank and extending to the inside of the water tank body by passing through the rear surface of the water tank; and a connection pipe provided in the water supply case and at a position corresponding to the suction pipe and connected to a pump, and wherein the suction pipe and the connection pipe are capable of selectively being connected to or disconnected from each other, and when the water tank is mounted, the suction pipe is configured to be connected with the connection pipe. a cabinet having a cultivating space thereinside; a door to open or close the cultivating space; at least one bed provided in the cultivating space and used to cultivate the plants; a light assembly to irradiate the bed with light for photosynthesis; a machine compartment provided at a lower portion of the cabinet, separated from the cultivating space and disposed to receive a compressor and a condenser which form a cooling cycle to control a temperature of the cultivating space; a step part protruding inward of the cultivating space from a position corresponding to the machine compartment; a water supply case disposed in front of the step part; and a water tank to store water to be supplied to the at least one bed, wherein the water tank is provided inside the cultivating space spaced apart from the machine compartment and in front of the water supply case, wherein the water tank is received inside a space defined by the door, the step part, the at least one bed, and a floor of the cultivating space, characterized in that the apparatus further comprises: tank rails disposed at opposite sides of the water tank and coupled to the water tank to withdraw or introduce the water tank; a suction pipe provided inside the water tank and extending to the inside of the water tank body by passing through the rear surface of the water tank; and a connection pipe provided in the water supply case and at a position corresponding to the suction pipe and connected to a pump, and wherein the suction pipe and the connection pipe are capable of selectively being connected to or disconnected from each other, and when the water tank is mounted, the suction pipe is configured to be connected with the connection pipe. tank rails disposed at opposite sides of the water tank and coupled to the water tank to withdraw or introduce the water tank; a suction pipe provided inside the water tank and extending to the inside of the water tank body by passing through the rear surface of the water tank; and a connection pipe provided in the water supply case and at a position corresponding to the suction pipe and connected to a pump, and wherein the suction pipe and the connection pipe are capable of selectively being connected to or disconnected from each other, and when the water tank is mounted, the suction pipe is configured to be connected with the connection pipe.