1. A non-transitory computer readable medium having stored thereon a character string updated degree evaluation program allowing a computer to execute: an extraction step of extracting common part character strings each comprising successive plural characters and each having a length greater than or equal to an arbitrary threshold value from original and updated texts subjected to comparison with each other; a step of arranging the common part character strings in an order that the common part character strings occur in the respective texts, to create divided lines; and a step of comparing the divided lines with each other, calculating a minimum number of substitution among the common part character strings necessary to cause one divided line to match another divided line, thereby acquiring a context edit distance, comprising: a step of subtracting 1 from a number of extracted common part character strings to acquire an edited point number as a number of edited points where editing is performed; a step of calculating a rate of a total length of remaining character strings obtained by eliminating the common part character strings from the text with respect to a total length of that text; a step of collecting remaining character strings obtained by eliminating the common part character strings from each text to create a non-common part character string set, and a novelty degree evaluation step of acquiring a new creation novelty degree DO which is a non-matching rate of an N-gram in a length less than the threshold value among non-common part character string sets, wherein the new creation novelty degree DO is expressed by DO=1−|Γ 1 ∩Γ 2 |/| 1 | (where Γ 1 and Γ 2 are N-gram sets each created from a non-common part character string set, |Γ 1 ∩Γ 2 | is a number of common elements commonly occurring in the N-gram sets Γ 1 and Γ 2 , and |Γ 1 | is a total number of N-grams contained in the N-gram set Γ 1 ); and a step of calculating a character string updated degree from an evaluation equation: a·EP+b·CED+NCP·DO·L (where EP is a number of edited points, CED is a context edit distance, NCP is a new creation percentage, DO is a new creation novelty degree, L is a total length of an updated text, and a and b are arbitrary coefficients), using the number of edited points, the context edit distance, the new creation percentage, and the new creation novelty degree.