1. A device for encoding a DPCM image comprising: a smoothness testing part for evaluating a smoothness in the vicinity of a pixel to be encoded at the current time; a prediction part for performing linear prediction, and prediction by using self-likeness of an image, to an original image, to obtain a predicted value; a quantization part for quantizing a prediction error between the predicted value and the original image; and, an encoding part for encoding the quantized information to arithmetic encoding depending on a result of the smoothness evaluation.