A cardiac output support apparatus comprising: a diaphragm whose size is set to fit an external shape of a lower heart part of a target person and which is composed of a flexible membrane that is responsive to a gas pressure; a plurality of compression balloons (12A to 12D) which are pasted at specified positions of an inner wall surface of the diaphragm so that the compression balloons are positioned opposite atriums and ventricles of a heart, respectively, when the lower heart part is covered and wrapped with the diaphragm; a first drive unit that is driven to press gas into the diaphragm; second drive units (23A to 23D) that are driven to eject or absorb a fluid to or from the compression balloons, respectively; and a tubular joint with a hollow part in which the diaphragm and each of the compression balloons are collectively stuffed in advance, wherein the first drive unit is configured to, in a state where a top end of the tubular joint is interposed in a chest of the target person and is located at the lower heart part, push the diaphragm out from the top end of the tubular joint while pressing the gas into the diaphragm, and to simultaneously cause the diaphragm to start flexing to cover and wrap the lower heart part, and to then stop pressing the gas into the diaphragm at a time point where the compression balloons are positioned at the atriums and the ventricles of the heart, respectively; and wherein the second drive units are configured to support a pumping function of the heart by alternately repeating an ejecting operation to fill each of the compression balloons with the fluid and cause each compression balloon to expand and an absorbing operation to cause each compression balloon to discharge the fluid and contract. a diaphragm whose size is set to fit an external shape of a lower heart part of a target person and which is composed of a flexible membrane that is responsive to a gas pressure; a plurality of compression balloons (12A to 12D) which are pasted at specified positions of an inner wall surface of the diaphragm so that the compression balloons are positioned opposite atriums and ventricles of a heart, respectively, when the lower heart part is covered and wrapped with the diaphragm; a first drive unit that is driven to press gas into the diaphragm; second drive units (23A to 23D) that are driven to eject or absorb a fluid to or from the compression balloons, respectively; and a tubular joint with a hollow part in which the diaphragm and each of the compression balloons are collectively stuffed in advance, wherein the first drive unit is configured to, in a state where a top end of the tubular joint is interposed in a chest of the target person and is located at the lower heart part, push the diaphragm out from the top end of the tubular joint while pressing the gas into the diaphragm, and to simultaneously cause the diaphragm to start flexing to cover and wrap the lower heart part, and to then stop pressing the gas into the diaphragm at a time point where the compression balloons are positioned at the atriums and the ventricles of the heart, respectively; and wherein the second drive units are configured to support a pumping function of the heart by alternately repeating an ejecting operation to fill each of the compression balloons with the fluid and cause each compression balloon to expand and an absorbing operation to cause each compression balloon to discharge the fluid and contract.