2. The document checking apparatus according to claim 1 , wherein the second determining includes determining, when it is determined that the number of the common elements is not less than the first similarity determination number, whether a number of a group of at least three or more character strings that appears within the same predetermined range is not less than a second similarity determination number.
2. The document checking apparatus according to claim 1 , wherein the second determining includes determining, when it is determined that the number of the common elements is not less than the first similarity determination number, whether a number of a group of at least three or more character strings that appears within the same predetermined range is not less than a second similarity determination number. 3. The document checking apparatus according to claim 2 , wherein the process further comprises rejecting, when it is determined that the number of the group of at least three or more character strings that appears within the same predetermined range is not less than the second similarity determination number, transmission to another transmission partner other than a transmission permit partner of the target document.