An imaging device has an image pickup section, a compression processing section, a correlation data holding section, and first and second calculating sections. The image pickup section generates photographic image data. The compression processing section performs compression processing on photographic image data. The correlation data holding section holds plural correlation data on changes in scale factor and compressed data amount of sample image data. The first calculating section calculates initial scale factors from standard correlation data generated from image data including high-frequency components most among sample image data and target compressed data amount. The second calculating section determines whether recompression processing by use of a different scale factor is necessary from a difference between target compressed data amount and compressed photographic image data amount and calculates the scale factor based on compressed photographic image data and correlation data at recompression processing such that the data compression rate decreases.