A mixing apparatus for dialysis comprising: a main unit that circulates or contains a main liquid; an auxiliary flow route that circulates an auxiliary liquid and whose tip is connected to the main unit; a pressurizing device (15, 23) that circulates the auxiliary liquid in the auxiliary flow route toward the main unit; and a switching device (16, 20, 24) that is arranged near a portion in the auxiliary flow route, which is connected to the main unit, and that can optionally turn on and off the auxiliary flow route, wherein the mixing apparatus is arranged such that when mixing the auxiliary liquid with the main liquid, pressure injection of the auxiliary liquid is performed on the main unit through the auxiliary flow route by turning on the switching device (16, 20, 24) and operating the pressurizing device (15, 23), and when not mixing the auxiliary liquid with the main liquid, the switching device (16, 20, 24) is turned off and the pressurizing device (15, 23) is stopped, and characterized in that the mixing apparatus further comprises: a discharge flow route that consists of a flow route branched from between the switching device (16, 20, 24) in the auxiliary flow route and the pressurizing device (15, 23) and that can discharge the main liquid or the auxiliary liquid; and a pressure control unit that can control a flow route between the switching device (16, 20, 24) and the pressurizing device (15, 23) in the auxiliary flow route to have a pressure lower than that of the main unit, when not mixing the auxiliary liquid with the main liquid. a main unit that circulates or contains a main liquid; an auxiliary flow route that circulates an auxiliary liquid and whose tip is connected to the main unit; a pressurizing device (15, 23) that circulates the auxiliary liquid in the auxiliary flow route toward the main unit; and a switching device (16, 20, 24) that is arranged near a portion in the auxiliary flow route, which is connected to the main unit, and that can optionally turn on and off the auxiliary flow route, wherein the mixing apparatus is arranged such that when mixing the auxiliary liquid with the main liquid, pressure injection of the auxiliary liquid is performed on the main unit through the auxiliary flow route by turning on the switching device (16, 20, 24) and operating the pressurizing device (15, 23), and when not mixing the auxiliary liquid with the main liquid, the switching device (16, 20, 24) is turned off and the pressurizing device (15, 23) is stopped, and characterized in that the mixing apparatus further comprises: a discharge flow route that consists of a flow route branched from between the switching device (16, 20, 24) in the auxiliary flow route and the pressurizing device (15, 23) and that can discharge the main liquid or the auxiliary liquid; and a pressure control unit that can control a flow route between the switching device (16, 20, 24) and the pressurizing device (15, 23) in the auxiliary flow route to have a pressure lower than that of the main unit, when not mixing the auxiliary liquid with the main liquid. a discharge flow route that consists of a flow route branched from between the switching device (16, 20, 24) in the auxiliary flow route and the pressurizing device (15, 23) and that can discharge the main liquid or the auxiliary liquid; and a pressure control unit that can control a flow route between the switching device (16, 20, 24) and the pressurizing device (15, 23) in the auxiliary flow route to have a pressure lower than that of the main unit, when not mixing the auxiliary liquid with the main liquid.