Abstract: A temperature sensor of a simple construction using PTC devices which efficiently detects a temperature in a wide area of a planar heater is realized. The temperature sensor has excellent durability, manufacturability and installability and can be manufactured at reduced cost. For this purpose, the temperature sensor comprises a plurality of temperature detection chips formed flat, each using a PTC device, enclosed by a pressure resisting member, and connected in series by a temperature detection signal cable. The temperature sensor is further laminated between layers of an insulating film and, as a whole, formed like a ribbon.