A first heat flux sensor, which outputs a first sensor signal according to a heat flux passing therethrough, a second heat flux sensor, which outputs a second sensor signal according to a heat flux passing therethrough, a thermal buffer body, which has a predetermined heat capacity, and a heat releasing body, which has a predetermined heat capacity, are provided, and the first heat flux sensor, the thermal buffer body, the second heat flux sensor and the heat releasing body are arranged in this order from a sensing subject side. The first sensor signal, which corresponds to the heat flux between the sensing subject and the thermal buffer body, is outputted from the first heat flux sensor, and the second sensor signal, which corresponds to the heat flux between the thermal buffer body and the heat releasing body, is outputted from the second heat flux sensor.