To enable system change operation while maintaining system reliability without stopping parallel use of part of power transmission lines by predicting an optimal implementation available period in advance of the system change.

An embodiment comprises: an input part 10 for inputting implementation condition data regarding implementation of scheduled system change; a database input-output part 20 for inputting data to and outputting data from a database which stores specification data regarding the system change; a calculation processing part 30 for calculating implementation suitability and operation timing of the system change on the basis of implementation target data and the specification data; and an output part 40 for outputting the calculation results.