The present invention makes it possible to quickly identify a place where a hyperlink is located in a document being displayed, and to design the document without caring about the indication of the location of the hyperlink. When a control thread is activated, a transparent sheet generation unit stores a transparent sheet into a transparent sheet storage unit; a thread activation unit activates a display thread and a visualization thread to cause a position identifying unit to identify a position where a hyperlink exists in a document being displayed; and to cause a marker drawing unit to draw a marker at the position thus identified in the transparent sheet. When the display thread is activated, a display unit reads a transparent sheet from the transparent sheet storage unit, and displays the transparent sheet in a visible state which has been stored in a visibleness state storage unit. When the visibleness thread is activated, an instruction reception unit receives an instruction from a user, and a visualization unit stores the visibleness state of the transparent sheet into the visibleness state storage unit in response to the instruction.