1. A decoding method comprising: receiving encoded data, the encoded data including: a syntax describing a first syntax element including a number of reference images in a first reference image list and a second syntax element including a number of reference images in a second reference image list, a syntax describing a plurality of parameters that are obtained by using a common index commonly used for the first reference image list and the second reference image list, and a syntax describing a third syntax element including a maximum number of values taken by the common index; regenerating the third syntax element from the encoded data; obtaining the plurality of parameters using the regenerated third syntax element and the common index; performing a decoding process that uses a reference image and the plurality of parameters that are obtained, wherein the common index is used to obtain the reference image from the first reference image list and the second reference image list.