Recently, to enhance the reality of remote or multimedia communication, research about the transmission of tactile information which is called haptics has been developing. Haptic information consists of several elements such as sense of force, surface touch, or thermal sensation. As for the thermal sensation on which this paper focuses, it is important to know the amount of the heat inflow, which is defined in this paper as a heat flowing into a thermal device from outside. A heat flux sensor is generally used for the obtainment of the information. However, the heat flux sensor absorbs the heat because the sensor itself has a thermal capacitance. As a result, in a transient state of the thermal system, the information of heat inflow is altered and the accurate information is not fed back to the controller. This paper proposes a heat inflow observer, which is based on a disturbance observer and estimates the information of heat inflow. By the proposed method, the value of heat inflow information is fed back to the controller, and it is possible to control the heat inflow. The heat inflow control can be used for the transmission of thermal sensation. Several experiments are conducted to see the validity of the observer and the heat inflow control.