Recently the demand on high graphic ability has increased in handheld systems due to multimedia or game application. Conventional DVS (dynamic voltage scaling) methods focus on reducing energy consumption of CPU. They didn't consider the influence of multimedia accelerators to make DVS policies. From the preliminary experiment, we found that the conventional DVS algorithm is not optimal to a system with a multimedia accelerator in context of reducing energy consumption of the system. We propose a power management mechanism that guarantees both QoS and reduction of energy consumption by considering the relation between the frequencies of the CPU and the frequencies of the multimedia accelerator. The proposed mechanism is a DVS technique in context of multimedia accelerator. We experimented the proposed mechanism on a testbed equipped with Intel XScale processor and Intel 2700G multimedia accelerator. The experimental result shows that the proposed method reduces energy consumption of the system as much as by 33% compared to conventional CPU-only DVS algorithms.