In ubiquitous computing environments, quality of service (QoS) in overall system may be affected when context information with excessive or deficient quality/quantity is exchanged among various entities in the environments. In this paper, we propose an adaptive control scheme of context information delivery for ubiquitous services based on QoS and quality of context information (QoC). To achieve the advanced control, we compose each entity as highly autonomous and cooperative agents. The system with this scheme can adapt to a variety of real-world environments and is able to maintain user requirements for QoS. This paper especially focuses on the design and implementation of the proposed scheme. We also illustrate the effectiveness of our scheme with some initial experiments from a viewpoint of adaptability for the changes which occur in entities in real world.