In a video data decoding apparatus, only video information of decoding unit containing video data decoded by use of video data different from video data used to decode video data upon encoding is eliminated, and only correct video data can be outputted. Thus, when a picture is displayed in the reverse direction, the change of such picture in the reverse direction can be made smooth considerably. A motion decoder comprises decoding means (102), (103) for decoding video data of GOP, a rearrangement means (101) for rearranging GOP data, a selecting means (104) for selecting outputs from the decoding means (102), (103), a memory means (105) for storing an output from the selecting means (104), and a selecting means (107) for inhibiting the selecting means (104) from selecting GOP containing video data decoded by use of video data different from video data used upon encoding when the order in which video data of GOP are inputted is opposite to the order in which the video data of GOP are encoded upon encoding.