A character string detection device for detecting a character string including at least one character in an image, the character string detection device comprising: a low-order detection means for judging whether or not the image possibly includes a detection target character string based on whether or not at least one character in the detection target character string is detected in the image, wherein the low-order detection means is adapted to compare an image lowered in resolution from an original image and a low-order model that is preliminarily prepared for each character and indicates a feature of the corresponding character, so as to detect a character in the detection target character string, the low-order model having character features fewer than those of a high-order model; a clustering means for defining at least one cluster including at least a fixed number of pixel groups having similar colors based on color information included in each pixel configuring the image, if the low-order detection means judges that the image possibly includes the detection target character string; a clipping means for partitioning the image into a region of the pixel groups belonging to the cluster defined by the clustering means and a region of other pixel groups, and for generating a clipped image excluding the region of the other pixel groups from the image; a character string detection means for detecting each character in the detection target character string to be detected so as to detect the detection target character string in the clipped image generated by the clipping means by comparing said a high-order model with said clipped image, and a pixel plot means for plotting each pixel in a color space coordinate system based on the color information included in each pixel configuring the image; wherein the clustering means is adapted to define in the color space coordinate system a cluster including a pixel group having the pixels that are plotted in the color space coordinate system by the pixel plot means and that have a distance therebetween smaller than a first threshold, wherein the character string detection device further comprises: a cluster selection means for selecting a cluster to be processed by the clipping means and the character string detection means from the plurality of clusters defined by the clustering means; wherein the cluster selection means is adapted to select, from unprocessed clusters, a cluster having smallest dispersion of the pixel groups in the cluster in the color space coordinate system as the cluster to be processed. a low-order detection means for judging whether or not the image possibly includes a detection target character string based on whether or not at least one character in the detection target character string is detected in the image, wherein the low-order detection means is adapted to compare an image lowered in resolution from an original image and a low-order model that is preliminarily prepared for each character and indicates a feature of the corresponding character, so as to detect a character in the detection target character string, the low-order model having character features fewer than those of a high-order model; a clustering means for defining at least one cluster including at least a fixed number of pixel groups having similar colors based on color information included in each pixel configuring the image, if the low-order detection means judges that the image possibly includes the detection target character string; a clipping means for partitioning the image into a region of the pixel groups belonging to the cluster defined by the clustering means and a region of other pixel groups, and for generating a clipped image excluding the region of the other pixel groups from the image; a character string detection means for detecting each character in the detection target character string to be detected so as to detect the detection target character string in the clipped image generated by the clipping means by comparing said a high-order model with said clipped image, and a pixel plot means for plotting each pixel in a color space coordinate system based on the color information included in each pixel configuring the image; wherein a cluster selection means for selecting a cluster to be processed by the clipping means and the character string detection means from the plurality of clusters defined by the clustering means; wherein the cluster selection means is adapted to select, from unprocessed clusters, a cluster having smallest dispersion of the pixel groups in the cluster in the color space coordinate system as the cluster to be processed.