A method of judging a validity of data included using a check code included in the data, generates a final computation result of the check code of 1 data block using data in a last frame of this data block. The final computation result is compared with the check code of the data block, and information instructing the processing of data having a specific group identifier to be skipped is set if an error in the data having the specific group identifier is detected before the comparing of the check code. If this information is set, the computation of the check code of the data having the specific group identifier is skipped.