In order to acquire a suitable fingerprint image by correcting an elongated fingerprint image, a line sensor acquires fingerprint image as a plurality of line-shaped images. A computation unit computes a similarity value by use of an evaluation function for evaluating the degree of similarity between the line-shaped images. The similarity value represents the degree of similarity between a first line-shaped image and a second line-shaped image which serve as a similarity evaluation target and are included in the plurality of the line-shaped image. A compression unit compresses the first line-shaped image and the second line-shaped image when the similarity value is equal to or larger than a predetermined threshold value to generate a new line-shaped image. A generation unit generates the entire fingerprint image by combining the new line-shaped image with the other line-shaped images.