An image encoding device includes a dynamic range generator for outputting dynamic range data Dd1 of block image data Dc1, an average value generator for outputting average value data De1 of the block image data Dc1, a number-of-pixel reducing unit 20 for decreasing number of pixels of the block image data by reduction-number of pixels to generate reduced-number-of-pixel block image data Dc1′, an encoding parameter generator 18 for generating encoding parameter pa1 specifying a quantization bit rate and the reduction-number of pixels in accordance with the dynamic range data Dd1, a quantization threshold generator 19 for generating a quantization threshold value tb1, and an image data quantizer 21 for generating quantized image data Df1 from the reduced-number-of-pixel block image data Dc1′ with use of the quantization threshold value tb1.