The present invention makes it possible to effectively encode/decode position information of leaves or nodes in tree-structured information by using a less amount of bits. The coding device according to the present invention includes a branching layer discriminating portion for identifying a hierarchical layer in which a leaf or node and a preceding leaf or node are separately branched and a position information coding portion for outputting a code corresponding to the identified hierarchical layer as a position information code for the leaf or node. Namely, merely information indicating a hierarchical layer in which a current leaf or node and a preceding leaf or node are separately branched is encoded as the position information of the leaf or node, thus increasing the efficiency of encoding leaf or node positions in the tree-structured information.