An object of the invention is to provide a highly durable sheet-heating element that has flexibility for making a seat more comfortable, that alleviates load stress for a heater wire while being seated, and that prevents the heater wire from being disconnected.Since a sheet-heating element related to the invention has a configuration in which a base member (11) of a sheet-heating element (10) is made of a flexible non-woven, it is possible to obtain flexibility for making the seat more comfortable. Also, since a surface of the base member (11) is subjected to a calender process so as to harden the surface, it is possible to stably obtain a hardness of for preventing a heater wire (12) from being disconnected when the load stress occurs while being seated. Accordingly, it is possible to make the seat more comfortable and to obtain high durability for preventing the heater wire (12) from being disconnected when the load stress occurs while being seated.