A search expression is automatically generated for designating a target element for a Web page whose contents change according to a system state or the number of elements to be displayed. The search expression generation device comprises the model sentence accumulation unit which accumulates a plurality of model sentences of structured documents, the element designation unit which designates an element to be searched in a model sentence, the structured document analysis unit which analyzes a structure of a model sentence, and the search expression structuring unit which adds or deletes the element selected to or from a search expression, wherein the structured document analysis unit analyzes a structure of a model sentence to generate a search expression with a condition added which is common to a plurality of model sentences of the same kind.