To generate compressed image data which is more efficiently utilized when energy subtraction image data and radiation image data being an origin of the energy subtraction image data are transferred to an external device and stored in a recording medium, etc.

An energy subtraction image generator 10 generates bone part image data SB and soft part image data SS by receiving low energy image data SL and high energy image data SH. A compressing means A provided in compression equipment 20 receives the low energy image data SL and the high energy image data SH and performs compression in a reversible system with low compression rate to the respective pieces of image data and on the other hand, a compressing means B provided in the compression equipment 20 receives the bone part image data SB and the soft part image data SS, performs compression in a nonreversible system with high compression rate to the respective pieces of image data. The respective pieces of compressed image data are transferred to the external device 30.