According to an embodiment of the invention, there is provided an image decoder for decoding encoded image data in an image block unit, including: a storage device configured to store a DC component of a past image block coefficient as a prediction value; a predict circuit configured to predict a DC component of a current image block coefficient using the prediction value; an inversely quantizing circuit configured to inversely quantize an image block coefficient outputted from the predict circuit; and a saturation processing circuit to execute a saturation processing of an image block coefficient outputted from the inversely quantizing circuit. A DC component of the image block coefficient outputted from the inversely quantizing circuit and a DC component of the image block coefficient after execution of the saturation processing are respectively inputted to the storage device.