The present teachings provide a blood purification apparatus and a priming method, which can reduce or dispense with dedicated components used for automated priming and which can reduce manufacturing costs of a blood circuit while achieving the automated priming. The present teachings further provide a blood purification apparatus including a liquid level adjustment device that can optionally introduce or discharge air into or from an upper portion of a venous air trap chamber, a control device that can adjust a liquid level formed inside the venous air trap chamber to have the height at any desired position by operating the liquid level adjustment device, and a priming solution supplying line that can supply a priming solution to an arterial blood circuit and a venous blood circuit. As taught herein, during priming, the control device can fill the arterial blood circuit and the venous blood circuit with priming solution supplied from the priming solution supplying line by operating the liquid level adjustment device at any desired timing.
