A storage system and a power control method therefor, an adapter and power control therefor, and a storage controller and a control method therefor, that enable the enhancement of their reliability with simple configurations. The storage system and the power control method therefor are configured in such a manner that the storage controller transmits a predetermined start-up completion signal to the adapter and the adapter starts to operate after receiving the start-up completion signal. When the adapter initiates stop of operation, it transfers cache data to the storage controller and transmits a predetermined first signal to the storage controller, the storage controller makes storage devices store the cache data in response to the first signal from the adapter, transmits a predetermined second signal to the adapter, and stops operation, and the adapter stops operation after receiving the second signal.