There is disclosed a horizontal type hydrohoist, in which slurry is forced to feed under lower pressure into feed pipes which are connected to a transport pipeline at their one ends and to a high pressure clear water pump at the others, said pump being adapted to deliver clear water under a high pressure, after which clear water is transferred under a high pressure through said feed pipe from said high pressure clear water pump, thereby transferring said slurry. This hydrohoist system presents the provision of means for preventing mixing and its spreading at the boundary portion between slurry and water within the feed pipes. More particularly, a separator which is designed not to rotate during the transfer is inserted in the aforesaid boundary portion in a manner that the separator may be transferred together with fluid, thus preventing the mixing of water with slurry as well as the resultant spreading thereof. According to a further aspect of the invention, at the completion of the slurry transfer under a high pressure, the separator is caused to be gradually slowed down to stop for the purpose of obviating a water hammer phenomenon within the pipings. In addition, after the removal of the slurry remaining around the separator by using a high pressure water, the feeding of the high pressure water is interrupted, thereby preventing mixing and its spreading at the boundary portion of water with slurry at the time of the subsequent introduction of slurry under lower pressure.