A heat flow sensor includes a heat transfer layer that has first and second surfaces confronting each other and has flexibility and a temperature difference measurement unit that measures a temperature difference between the first and second surfaces of the heat transfer layer. The heat transfer layer includes a first member having flexibility and a second member with higher thermal conductivity than the first member. The thickness of the heat transfer layer is equal to or greater than 0.5 mm, thermal conductivity of the heat transfer layer is equal to or greater than 10 W/ (m×K), and Shore hardness of the heat transfer layer is equal to or less than A50.
