A device that warms a surface of a living body required to be warmed at an appropriate timing at any place indoors and outdoors or the sea without causing low temperature burns. A sheet having a heat generating function including a circuit capable of receiving electric power without contact over a sheet containing plastic or a fibrous body, a heat generating circuit, and a circuit that controls the temperature of the heat generating circuit is manufactured. The user with the sheet transmits the radio signal from the transmission device outdoors or indoors to heat the heat generating circuit on the sheet and the heat can be conducted to the skin of the user. Temperature can be automatically adjusted by the circuit for controlling the temperature of the heat generating circuit.