A blood purification apparatus comprising: a blood circuit including an arterial blood circuit and a venous blood circuit through which blood of a patient is allowed to be extracorporeally circulated; a blood purification device provided between the arterial blood circuit and the venous blood circuit and that purifies the blood flowing in the blood circuit; a tube section including a dialysate introduction line and a dialysate drain line through which dialysate is introduced into and drained from the blood purification device, respectively; a pressure-detecting device that is capable of detecting a pressure in the tube section (γ) or a pressure in the blood circuits(α,β); a communicating line (La, Lb) connected to the tube section and to the blood circuit and that allows a flow route of the tube section and a flow route of the blood circuit to communicate with each other; and a control device that is capable of controlling opening and closing of any of clamping devices included in the tube section or in the blood circuit and operation of any of pumps included in the tube section or in the blood circuit, characterized in that the control device that performs the controlling is capable of executing a pressure-applying step: in which a negative pressure or a positive pressure is applied to the flow route of one of the tube section and the blood circuit; a propagating step in which the negative pressure or the positive pressure applied in the pressure-applying step is propagated to the flow route of an other of the tube section and the blood circuit through the communicating line; and a checking step in which whether or not the propagation of the negative pressure or the positive pressure in the propagating step is successful is checked with reference to the pressure detected by the pressure-detecting device, and in which whether or not the connection of the communicating line is appropriate is checked with reference to whether or not the propagation of the negative pressure or the positive pressure is successful. a blood circuit including an arterial blood circuit and a venous blood circuit through which blood of a patient is allowed to be extracorporeally circulated; a blood purification device provided between the arterial blood circuit and the venous blood circuit and that purifies the blood flowing in the blood circuit; a tube section including a dialysate introduction line and a dialysate drain line through which dialysate is introduced into and drained from the blood purification device, respectively; a pressure-detecting device that is capable of detecting a pressure in the tube section (γ) or a pressure in the blood circuits(α,β); a communicating line (La, Lb) connected to the tube section and to the blood circuit and that allows a flow route of the tube section and a flow route of the blood circuit to communicate with each other; and a control device that is capable of controlling opening and closing of any of clamping devices included in the tube section or in the blood circuit and operation of any of pumps included in the tube section or in the blood circuit, characterized in that the control device that performs the controlling is capable of executing a pressure-applying step: in which a negative pressure or a positive pressure is applied to the flow route of one of the tube section and the blood circuit; a propagating step in which the negative pressure or the positive pressure applied in the pressure-applying step is propagated to the flow route of an other of the tube section and the blood circuit through the communicating line; and a checking step in which whether or not the propagation of the negative pressure or the positive pressure in the propagating step is successful is checked with reference to the pressure detected by the pressure-detecting device, and in which whether or not the connection of the communicating line is appropriate is checked with reference to whether or not the propagation of the negative pressure or the positive pressure is successful. a pressure-applying step: in which a negative pressure or a positive pressure is applied to the flow route of one of the tube section and the blood circuit; a propagating step in which the negative pressure or the positive pressure applied in the pressure-applying step is propagated to the flow route of an other of the tube section and the blood circuit through the communicating line; and a checking step in which whether or not the propagation of the negative pressure or the positive pressure in the propagating step is successful is checked with reference to the pressure detected by the pressure-detecting device, and in which whether or not the connection of the communicating line is appropriate is checked with reference to whether or not the propagation of the negative pressure or the positive pressure is successful.