1. An information searching method to be implemented in a computer, comprising: a selection accepting procedure accepting a first character string from characters or a character string in a reading or inspecting document that is displayed on a display unit; an index information acquiring procedure acquiring a second character string from index information for searching the reading or inspecting document, based on identification information of the reading or inspecting document; and a search control procedure executing a search based on the first character string and the second character string.