PURPOSE: To enable the saving of power, by dinamically reconstituting the system according to the load condition of system and cutting off the power supply through disconnecting unnecessary devices.

CONSTITUTION: The load of CPUs CP1, CP2 is reduced in a computer system 1 and it is detected, then the CPU to be cut off, e.g., CP2 is determined, and the job in the CPU CP2 is shared to the CPU CP1, and in the CPU CP2 to be cut off, when the job to be processed is absent, the constitution control register in the constitution controller CC is changed, allowing to cut off the CPU CP2 from the system constitution so that it can not give any effect to other devices. After that, through the constitution controller CC and service processor SP, the instruction to cut off the power supply for the CPU CP2 cut off is given to the power supply controller PC, allowing the power supply controller PC receiving the instruction to cut off the power supply for the CPU CP2 to be cut off.