In a video scalable encoding method, based on encoding information of an immediately-lower image region in an immediately-lower layer, which is present at spatially the same position as an encoding target image region, a data structure of the weight coefficient, that includes a proportional coefficient and an offset coefficient, is determined. When the immediately-lower image region performed interframe prediction in the immediately-lower layer, the method identifies an immediately-lower layer reference image region that the immediately-lower image region used as a prediction reference for motion prediction, and calculates the weight coefficient by applying a weight coefficient that the immediately-lower image region used in weighted motion prediction to a DC component of an image region in the upper layer, which is present at spatially the same position as the immediately-lower layer reference image region, and assuming a result of the application as a DC component of the immediately-lower image region.