Abstract: A line image detection apparatus having an image input function for inputting an image on a document. The image includes a rectangular character string and a linear line drawn along the character string. The line detection apparatus has a function for detecting a character string image from the image, a function for forming a projection image on the basis of the distance from a lower end of the character string image to each first black pixel found in the character string image in the vertical direction, and a function for comparing the distance from the lower end of the character string image to each first black pixel, with a predetermined threshold value, thereby to define a plurality of "slice 0" areas included in the projection image. The distance, in each of the "slice 0" areas, from the lower end of the character string image to each first black pixel is lower than the predetermined threshold value.