1. A key word detection device for detecting a search key word from a target image in order to perform a search with a search engine on the internet, the key word detection device comprising: a processor configured to operate as: a feature point detector configured to detect a feature point of a specific character string from the target image, the specific character string prompting a user to perform the search; a key word recognition unit configured to recognize a character string existing in surroundings of the feature point detected by the feature point detector as the search key word in the target image; a storage for storing character information and data of the target image used by the processor; and a search window detector configured to detect a search window from the surroundings of the feature point detected by the feature point detector in the target image, the search window being used to input the search key word; wherein the key word recognition unit is configured to recognize a character string in the search window detected by the search window detector as the search key word, and the search window detector is configured to, in the target image, detect presence of the search window in a neighborhood of the recognized character string according to a detection priority order set based on specific detection directions from the character string.