To provide a thermal developing device in which the image of proper density is always supplied by eliminating influence to developing density caused by temperature change or the like at the inside of a device and also its controlling method.

This method is the controlling method of the thermal developing device to thermally develop film on which a latent image is formed by feeding heat developable photosensitive film and forming the latent image on the film by exposing based on an image signal. A film package is loaded in the thermal developing device (S01). It is decided whether or not to perform correction with respect to the density of film in the package (S03). The latent image is formed by exposure on the film based on a test image signal for measuring the density and is thermally developed in performing the correction with respect to the density (S05). The density information of the developed test image for measuring the density of the film is obtained (S06), so that the correction with respect to the density is performed so as to correct a difference from desired density based on the density information of a test image for measuring the density (S07). Also, it is decided whether or not to perform the correction again after performing the correction with respect to the density (S10).