Powder A dissolving means 1 and powder B dissolving means 1 prepare a solution A and a solution B by dissolving a dialysis powder A and a dialysis powder B, respectively, in purified water. The solution A and the solution B with prescribed concentrations are prepared beforehand so that a dialysate can be obtained by mixing the solution A and the solution B in the prescribed proportions without the addition of purified water. Weighing means 4 of a dialysate preparation device 3 feeds the solution A and the solution B to a reciprocating pump 5 so that the solutions are mixed in the prescribed proportions, and in the reciprocating pump 5 the solution A and the solution B with the set concentrations are mixed in the prescribed proportions, whereby it is possible to prepare the dialysate without adding purified water. Dialysates can be easily prepared.
