Recently, with the increasing use of various kind of portable devices, such as notebook computers, PDAs(Personal Data Assistants), PMPs(Portable Media Players) and etc., a power consumption problem -how long such devices can run with their rechargeable battery- is one of the key issues in the portable device industry. Much research has resulted in new chip technologies for low-power consumption and, because of this, the battery life of portable devices today is longer than ever before. On the one hand, research into low-power chips is producing some effective results, but on the other hand, research through the software approach have not brought about significant results, except possibly for techniques, such as hibernation and turning off LCDs. In this paper, we propose a dynamic power management system that considers process status, battery characteristics and application program types together, to raise the effectiveness of power management. The experimental results, using the proposed system, show that an 11% decrease in power consumption can be obtained.