To solve a problem with a conventional auxiliary artificial heart in which red blood cell fragmentation or a thrombus is likely to occur due to contact of circulating blood with an instrument part, resulting in necessity of long-term administration of an antithrombotic agent and easy development of various complications.

The ejection power of the heart 1 is strengthened by transmitting a force of a pump driven by electric power to the cardiac chamber from the outside of the heart 1. This allows avoidance of invasion to the heart or major blood vessel system and the contact of an instrument with circulating blood. Concretely, the heart is covered with a hollow saccular interface, and the internal pressure of the interface is increased in a contraction phase to assist the contraction of the heart. The internal pressure is reduced in a diastolic phase. The change of the internal pressure is performed by sending and removing the content by the drive pump through a hollow tube provided in a part of an outside membrane 3.