1. A processor-implemented software modification estimate method of calculating total man hours of software modification prior to modification work based on an initial data group being numerical data serving as an index of a modification degree which is preset in a terminal, and an estimate element group being numerical data indicating contents of modification newly input to through terminal by a user, when development by modification of existing software is performed for software development, the software modification estimate method comprising: an input data recognition sequence of recognizing the estimate element group input to the terminal by the user; a modification scale distribution table generation sequence of generating, as a modification scale distribution table, a table indicating a relationship between the initial data group and a modification net scale numerically expressed from an actual modification sale included in the estimate element group, and analyzing the modification scale distribution table to derivate a distribution number of modification parts present in each development unit in the modification development; an estimate table generation sequence of calculating a development scale, which is a product amount produced by the modification, and a productivity produced by the modification, based on the estimate element group, the distribution number, and the modification net scale; generating, as an estimate table, a contrast among the development scale, the productivity, and the estimate element group; and estimating a man-hour of the modification based on the estimate table; a data receiving/transmitting sequence of receiving and transmitting an appropriate data group among the initial data groups held in the terminal in response to a call from the table generation sequence when the modification scale distribution table and the estimate table are generated; and an output sequence of visually displaying the derived estimate result and the respective tables generated in the modification scale distribution table generation sequence and the estimate table generation sequence, wherein the modification distribution number is determined as a number suitable for a modification base proficiency degree obtained by setting the modification target range, the modification distribution degree, and a proficiency of the modification base to have an arbitrary value, by matching the modification net scale in blocks with the modification scale distribution table when the modification base is separated by an arbitrary number to form blocks.