1. An image coding method for coding a current block included in a current picture, the picture coding method comprising: referring to a first list in which smaller indices are assigned to pictures preceding the current picture in display order than indices assigned to pictures following the current picture, the first list being a list of index associating blocks included in the current picture with each picture that is referred to by the blocks; selecting, from the first list, as a first reference picture, a picture with the smallest index out of a plurality of pictures that are referred to by a plurality of neighboring blocks, the plurality of neighboring blocks being at the neighborhood of the current block in the current picture; referring to a second list in which smaller indices are assigned to pictures following the current picture in display order than indices assigned to pictures preceding the current picture, the second list being a list of index associating blocks included in the current picture with each picture that is referred to by the blocks; selecting, from the second list, as a second reference picture, a picture with the smallest index out of the plurality of pictures; and predictive-coding the current block by referring to the first reference picture and the second reference picture.