The invention provides a system state arithmetic device, a method and a system, a system control device and a method, and a power distribution trend simulation device and a method. The power distribution trend simulation device (100) is provided with a power system trend calculation part (10) which calculates the power trend in a power system from a transformer substation (1) to a pole transformer through using the loading power of the pole transformer (5), a user load simulation part (80) which calculates the time change of the loading power used by a user, a scattered power simulation part (90) which calculates the time change of the power generated by a scattered power supply, and a system state management part (30) which manages the calculation process. The system state management part provides loading power requirement information added with the time information for the user load simulation part and the scattered power simulation part and makes the user load simulation part and the scattered power simulation part process the information. The time interval is determined according to the time change rate calculated by the user load simulation part and the scattered power simulation part.