Spin current has been attracting recent interest, and it has been discussed separately from the heat current. Nevertheless, we note that there is a hidden relationship between the physics of spin current and that of heat current. In the present research, by unifying these two fields of transport, we deepen our understanding on thermoelectrics and spintronics, and explore novel physical phenomena. We pursue thermoelectric materials and devices based on new physics principles and improve the existing devices of such kind. We also evaluate Joule heating in spintronics devices, and explore a way to minimize it.