A device for estimating a standard character width in a character string, the device comprising: a character string image acquiring unit for acquiring a character string image; a measurement of character width acquiring section for acquiring measurements of character width by measuring character widths in a character string direction with respect to a plurality of characters from the character string image acquired by the character string image acquiring unit; a character provisional recognition section for provisionally recognizing characters having the measured character widths through a provisional matching process; and a standard character width determining section for determining a standard character width based on the measurements of character width of the provisionally recognized characters, wherein the standard character width is an average character width; wherein the provisional matching process is assumed to correctly recognize a character if the matching reliability is greater than or equal to a predetermined threshold value, wherein, if the character provisionally recognized by the provisional matching process is a combination character formed by combining two kanji radicals arranged in the character string direction of the character string image, the standard character width determining section excludes the measurement character width of the combination character from the measurement character width used to determine the standard character width, wherein, if the character provisionally recognized by the provisional matching process is a kanji radical for forming one combination character when combined with a character either in front or back in the character string direction with respect to the character, the standard character width determining section excludes the measurement of character width of the kanji radical from the measurement of character width used to determine the standard character width, and wherein, if the exclusion of the measurement character width of the combination character or of the kanji radical results in the measurement character width used to determine the standard character width being zero, the standard character width determining section determines the standard character width based on the character width in a direction perpendicular to the character string direction. a character string image acquiring unit for acquiring a character string image; a measurement of character width acquiring section for acquiring measurements of character width by measuring character widths in a character string direction with respect to a plurality of characters from the character string image acquired by the character string image acquiring unit; a character provisional recognition section for provisionally recognizing characters having the measured character widths through a provisional matching process; and a standard character width determining section for determining a standard character width based on the measurements of character width of the provisionally recognized characters, wherein the standard character width is an average character width; wherein the provisional matching process is assumed to correctly recognize a character if the matching reliability is greater than or equal to a predetermined threshold value, wherein, if the character provisionally recognized by the provisional matching process is a combination character formed by combining two kanji radicals arranged in the character string direction of the character string image, the standard character width determining section excludes the measurement character width of the combination character from the measurement character width used to determine the standard character width, wherein, if the character provisionally recognized by the provisional matching process is a kanji radical for forming one combination character when combined with a character either in front or back in the character string direction with respect to the character, the standard character width determining section excludes the measurement of character width of the kanji radical from the measurement of character width used to determine the standard character width, and wherein, if the exclusion of the measurement character width of the combination character or of the kanji radical results in the measurement character width used to determine the standard character width being zero, the standard character width determining section determines the standard character width based on the character width in a direction perpendicular to the character string direction.