PURPOSE: To make possible interactive operation for changing analytic conditions halfway without altering an analytic code main body by providing an input generating means for restarting which generates input data for restarting for changing calculation conditions.

CONSTITUTION: A state corresponding to respective data of a plant is displayed on a monitor screen with the output from a screen display program 15. While locking at the monitor screen, operation (a) for changing the calculation conditions is performed for the screen display program 15 by using a mouse, etc. The screen display program 15 outputs desired input data to an input generating program 16 for restarting together with a calculation condition change instruction. The input generating program 16 for restarting generates input data 17 for restarting including the desired input data on the basis of the original input data 10. The data is inputted to an analytic code 11 and restart calculation is performed according to data 17 changed in the conditions.