A prediction information derivation unit derives inter prediction information candidates from inter prediction information of coded prediction blocks neighboring a prediction block subject to coding within the same picture as the prediction block subject to coding and inter prediction information of a prediction block in a coded picture that is different from the prediction block subject to coding. The prediction information derivation unit determines an inter prediction information candidate to be used for inter prediction of the prediction block subject to coding from the inter prediction information candidates that have been derived. A second bitstream generation uni codes an index that indicates the inter prediction information candidate based on the number of the inter prediction information candidates.