1. An information management method in which a computer manages information, comprising: responsive to information input, the computer storing information for each of a plurality of nodes in a document file, the nodes including node data with node identification information for identifying the nodes; responsive to the selection of a node, identifying a parent node of the node using data included in the node data; calculating values for node variable data in need of calculation by executing a script for substitution included in the node data, the script for substitution using node data of the node and node data of a lineal upper node of the node; and displaying a tree structure of the node using node data of the parent node and the node data of the node; displaying the script for substitution for editing; responsive to an edit of the script for substitution and selection of a button, re-calculating values for node variable data in need of calculation by executing the edited script for substitution; and re-displaying the tree structure of the node; wherein the document file includes reference information indicating a relation between a reference destination node and a reference source node inputted to the computer, and the script for substitution of the reference source node obtains a value of self node variable data by performing computation using variable data of the reference destination node.