We present Sensos, a sensor node operating system with the device management scheme for sensor nodes with multiple sensor elements. As the number of sensor elements attached to a single sensor node increases, programming of applications for each sensor elements becomes a significant burden to the developer. A device management scheme providing well-defined APIs independent to a specific sensor element itself can make the program development more efficient and convenient. The basic concept of the device management scheme integrated in this proposed sensor node operating system, Sensos, is based on IEEE 1451 standard. We redefined and simplified the existing standard to make it applicable to the sensor node operating system. Implementation of Sensos shows a remarkable small footprint less than 55Kbytes and we demonstrate that applications for new sensor devices can be easily developed using the proposed Sensos.