The apparatus comprises a case, a magnetic member which is provided at a bottom surface of the case and attaches the case to the outer surface of the cooking vessel by forming an attractive force with respect to the outer surface of the cooking vessel, first and second temperature sensors which are disposed at the bottom surface of the case while being spaced a predetermined distance apart from each other in the vertical direction, and measure temperatures of two measurement points located at the outer surface of the cooking vessel and spaced the predetermined distance apart from each other in the vertical direction, respectively and a controller which is provided in the case and estimates the temperature of the food based on an average value of the temperatures measured respectively by the first and second temperature sensors and a desired temperature value provided by a user.