1. A moving picture decoding method for using an inter prediction process, the method comprising: a first step to receive encoded information of a target block to be decoded by the 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 whether the target block is encoded by a motion-vector combined area mode or not; a fourth step to determine a motion vector for the target block, wherein when the target block is encoded by the motion-vector combined area mode, the motion vector for the target block is 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; a fifth step to generate a prediction image for the target block by using the determined motion vector; and a sixth step to generate a decoded image of the target block based on the prediction image generated in the fifth step and the prediction difference data decoded in the second step.