1. A translation display apparatus comprising: a document image acquiring section that acquires a document image of a document containing a sentence composed of a plurality of lines in a first language; a character recognizing section that extracts a text area from the document image, recognizes first language characters included in the extracted text area, and specifies positions of the first language characters in the document image; a translated language character string creating section that creates a translated language character string by translating an original character string which is a first language character string including the first language characters recognized by the character recognizing section, into a second language; a translated language character string positioning section that places the translated language character string so as to be in a position which is close to the original character string and in inter-line space between first language character strings in the document image, based on the positions of the first language characters specified by the character recognizing section; an image creating section that creates an image of a translated sentence-added document in which the translated language character string is disposed in the document image at the position placed by the translated language character string positioning section; a display section that displays the image of the translated sentence-added document created by the image creating section; an enlargement display instruction input section that receives an instruction to enlarge and display a part of the image of the translated sentence-added document displayed on the display section; a partially-enlarged image creating section that creates a partially-enlarged image in which a part of the image of the translated sentence-added document is enlarged on the basis of the instruction inputted from the enlargement display instruction input section; and a control section that controls the image creating section and the display section, the control section controlling the image creating section to create a partial enlargement-added image which is an image obtained by superimposing the partially-enlarged image on the image of the translated sentence-added document, and controlling the display section to display the partial enlargement-added image when the instruction of enlargement display is inputted from the enlargement display instruction input section, wherein the partially-enlarged image creating section creates the partially-enlarged image by adding the original character string to the position in the interline space between first language character strings in the image of the translated sentence-added document in an edible state, and the control section controls the image creating section to create the partial enlargement-added image by superimposing the partially-enlarged image, to which the original character string is added in an edible state, on the image of the translated sentence-added document and controls the display section to display the partial enlargement-added image.