The present article reviewed a variety of studies on endorphin to understand properly the relation between endorphin and health. Endorphin is an endogenous morphine released for pacifying the body when a body is under pain or in need of oxygeon, and when a person is uncomfortable due to psychological shock. Its mechanism works in a way contrary to the understanding held by the general public, in which endorphin is released when a person is satisfied and cheerful. Thus, it is necessary to understand the function of endorphin properly.