A system LSI contains a main circuit and an eDRAM. The main circuit contains a standby controlling circuit and a CPU. Each circuit block receives power through independent power lines. Power is always supplied to the standby controlling circuit. When the system LSI has entered a standby state, power to the main circuit is turned off. Only when the eDRAM is used, power is supplied thereto. The standby controlling circuit and a power controlling circuit control power supplied to each circuit block. When there is no task the CPU has to process, the system LSI enters the standby state from the operation state. When an operation input has taken place with an operating portion or when an input has taken place in an external input, the standby controlling circuit performs a process necessary for waking up the system LSI. Power is supplied to the main circuit.