To predict a present picture element through the use of the pattern of the picture element in the neighborhood by predicting the label of the picture element based on the comparison of probabilities which are decided for every basic pattern label and encoding the picture element based on a predicted label and an effective label.

When un-encoded picture element is recognized in the raster order arrayal, the extension pattern of the present picture element is decided (S102 and S103). Then, it is predicted that the present picture element is the same as that in the neighborhood, which is provided with the lowest label in a dictionary formula among the labels having a max. predicting probability in the decided extension pattern (S104). Unless the prediction is proved right, it is inspected which picture element other than the predicted in the neighborhood the present picture element is the same (S107). At the time of unsuccess in this test the value of the present picture element is added to an Anomaly List and, moreover, a symbol ANOMALY/-n is added to a Trend List (S109 and S110). Then, the prediction probability of the present extension pattern is updated based on the effective value of the present picture element (S111).