Peltier device has recently been attracting attention as a suitable device to produce thermal sensation. For the information obtainment of the heat exchanged between the device and external environment, heat flux sensor is generally utilized. However, heat flux sensor has drawbacks from the viewpoints of thermal capacitance and cost compared with temperature sensor. In order to address the problems, heat flux sensor-less estimation method of the heat flow should be developed. This research focuses on the distributed parameter system of Peltier device, and constructs a heat inflow observer based on the system. The derived model has the infinite number of poles and zeros, and the observer is approximated with the consideration on the poles and zeros for the simplicity in implementation. As shown in the experiments, the proposed observer shows its capacity of estimating heat inflow without using a heat flux sensor.