1. A moving picture decoding method comprising: a first step to receive encoded information of a target block to be decoded by an inter prediction process, the encoded information being encoded without a frequency transform process; a second step to decode prediction difference data of the target block from the encoded information without the frequency transform process; a third step to determine by which prediction mode the target block is encoded; a fourth step to generate a prediction image by the prediction mode determined by the third step, wherein if the target block is encoded by an intra prediction mode, a prediction image is generated by the intra prediction mode, and wherein if the target block is encoded by a motion-vector combined area mode, the prediction image is generated by using a motion vector determined so as to be in common with a motion vector of an adjacent block adjacent to the target block without adding a difference vector, based on a status of motion vectors of a plurality of adjacent blocks adjacent to the target block; and a fifth step to generate a decoded image of the target block based on the prediction image generated in the fourth step and the prediction difference data decoded in the second step.