An object of the present invention is to provide a blood purification apparatus and the method for inspecting liquid leakage therefrom which can perform a sufficient liquid leakage inspection over a whole region of the blood circuit. According to the present invention, there is provided a blood purification apparatus comprising a blood circuit including an arterial blood circuit arranged thereon a blood pump and a venous blood circuit for extracorporeally circulating blood of a patient by the blood pump a blood purification instrument for purifying the blood of a patient extracorporeally circulated through the blood circuit adapted to be connected with a base end of the arterial blood circuit and a base end of the venous blood circuit of the blood circuit a dialysate introducing line for introducing dialysate into the blood purifying instrument and a dialysate discharging line for discharging the dialysate from the blood purifying instrument characterized in that the blood purification apparatus further comprises a pressure varying means for varying pressure in a closed circuit under a condition in which the blood circuit is formed as a closed circuit of a sealed condition with connecting the tip end of the arterial blood circuit and the tip end of the venous blood circuit and a liquid leakage detecting means for detecting liquid leakage in the blood circuit in accordance with pressure variation generated by the pressure varying means.
