1. A method of creating classification pattern, the method comprising: extracting a partial character string including a reserved word and a character string immediately previous or subsequent to the reserved word from each of a plurality of pieces of target data, the plurality of pieces of target data conforming to a first pattern character string including the reserved word defined by a protocol; detecting target data including the partial character string among the plurality of pieces of target data; specifying a first partial character string from the extracted partial character string based on the detected target data; and creating, by a processor, a second pattern character string for classifying the plurality of pieces of target data based on the first pattern character string and the first partial character string.