1. A 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.