An artificial heart has a driving section, a nozzle section, a pump section for insertion into a ventricle of a human heart, and a sealing section forming a seal for a driving shaft extending from the driving section for driving the pump section. A sealing liquid chamber filled with a sealing liquid is formed around the driving shaft between the sealing mechanism and the driving section. The sealing liquid in the sealing liquid chamber maintains the sealing mechanism in a liquid-tight state and lubricates the sealing mechanism, whereby blood is prevented from entering the driving section. Even if blood happens to enter the driving section, the blood is mixed with the sealing liquid and does not coagulate. Thus, the operation of the artificial heart is not suppressed.