In a system for displaying a radiation image by scanning a recording medium carrying a radiation image stored thereon and converting the image into an electrical signal, an unsharp mask signal Sus corresponding to a super-low frequency at each scanning point is detected, and an operation, expressed as S'=Sorg+.beta.(Sorg-Sus) where Sorg denotes an original image signal detected from the recording medium and .beta. denotes an emphasis coefficient, is conducted to perform an unsharp masking process for emphasizing frequency components above the super-low frequency. The unsharp mask signal Sus and/or the emphasis coefficient .beta. is continuously changed to display the image as a moving image. The unsharp mask signal Sus is changed by calculating a basic unsharp mask signal Sus for a basic unsharp mask at a predetermined scanning point, and calculating a different unsharp mask signal Sus at the predetermined scanning point by simple arithmetic averaging of the basic unsharp mask signals Sus for basis unsharp masks surrounding the basic unsharp mask.