To easily construct a real time system and to shorten the development period of an application using the real time system.

The real time system designing device is provided with a user interface part 11 for receiving user's input data and presenting a parameter extraction result or the like to the user, a small scenario parameter extraction part 12 for extracting a parameter or the like indicating the start state or end state of a small scenario, a small scenario state information storage part 14 for storing various extracted parameters, a small scenario connection part/ consistency judgment part 13 for judging whether inconsistent operation is generated in the system at the time of connecting two small scenarios or not, and an inter-small scenario connection data storage part 15 for storing connection data between small scenarios.