A new approach for body heat energy harvesting was proposed, and the theoretical performance has been demonstrated for wearable health care sensors as a target. One of the most important issues in the wearable system is a power supply. Humans keep their body temperature constant as long as they are alive. If we use thermal energy effectively, we could get the energy no matter when and where we go. However, thermal energy has hardly been used as power supply because thermoelectric conversion efficiency is very low. Quite different from the conventional thermoelectric device, the new approach uses rotation of turbine by stack effect. The driving force for the turbine is the pressure difference (Delta P) created by stack effect in a closed system. To obtain high performance, the device parameters are optimized by theoretical analysis. The obtained power density is 97.2 mW/cm(3) when the outside air temperature is 277.15 K, and the device size is 5 mm x 2 mm x 10 mm. The energy density of the device is five or more times larger than that of a solar cell. The energy device can be assembled directly inside the various kind of wearable health care sensors. Therefore, the new approach for the body heat energy harvesting is a promising power supply means for the wearable system.