7. A document converting method for converting a first structured document to a second structured document different in structure from the first structured document, comprising: reading a template indicating a structure of the second structured document and described in a same language with the second structured document; displaying a design represented by the read template on a screen of a display device; allowing a user to specify an element or an element content configuring the template in the displayed design; allowing the user to define a correspondence definition indicating correspondence between an element in the first structured document and an element in the template by corresponding a tag of a element in the first structured document with a position of the specified element or element content in the displayed design; converting the template and the first structured document into tree structure objects, respectively; searching the specified element or the specified element content from the tree structure object of the template, sequentially searching the element described in the correspondence definition from the searched element or element content in the tree structure object of the template as a start point, and generating a tree structure object of the template which comprises the element sequentially-searched element; searching an element described in the correspondence definition from the tree structure object of the first structured document; and entering, when the element detected by searching from the tree structure object of the first structured document having a child element and a corresponding element in the template having a defined parent element, the generated tree structure of the template into the tree object of the template according to the number of child elements, and replacing, when the element detected by searching from the tree structure object of the first structured document having only an element content and a corresponding element in the template having no child element, the element content of the detected element with the specified element content in the template.
7. A document converting method for converting a first structured document to a second structured document different in structure from the first structured document, comprising: reading a template indicating a structure of the second structured document and described in a same language with the second structured document; displaying a design represented by the read template on a screen of a display device; allowing a user to specify an element or an element content configuring the template in the displayed design; allowing the user to define a correspondence definition indicating correspondence between an element in the first structured document and an element in the template by corresponding a tag of a element in the first structured document with a position of the specified element or element content in the displayed design; converting the template and the first structured document into tree structure objects, respectively; searching the specified element or the specified element content from the tree structure object of the template, sequentially searching the element described in the correspondence definition from the searched element or element content in the tree structure object of the template as a start point, and generating a tree structure object of the template which comprises the element sequentially-searched element; searching an element described in the correspondence definition from the tree structure object of the first structured document; and entering, when the element detected by searching from the tree structure object of the first structured document having a child element and a corresponding element in the template having a defined parent element, the generated tree structure of the template into the tree object of the template according to the number of child elements, and replacing, when the element detected by searching from the tree structure object of the first structured document having only an element content and a corresponding element in the template having no child element, the element content of the detected element with the specified element content in the template. 10. The document converting method according to claim 7 , wherein searching includes searching a structure in a direction of a parent element from a position of an specified element or an specified element content specified.