Abstract: Disclosed herein is a velocity and concentration adjustable coupling pipe apparatus equipped between a lifting pipe and a collector. The apparatus includes a coupling pipe having a lower inlet and an upper outlet which are different in diameter from each other. A seawater inlet pipe passes through a side surface of the coupling pipe to permit inflow of seawater. A slurry flow control valve is provided in the coupling pipe to control the inflow of slurry. A seawater flow control valve is provided in the seawater inlet pipe to control the inflow of the seawater. A first sensor measures concentration of slurry discharged through the upper outlet. A second sensor measures velocity of the discharged slurry. A third sensor measures velocity of slurry introduced into the lower inlet. A control panel controls the opening ratio of each of the slurry and seawater flow control valves.