We describe a new adaptive manager-side control policy for the contract net protocol that uses the capabilities of all agents in a massively multi-agent system (MMAS). Recent advances in Internet services, pervasive computing, and grid computing require sophisticated MAS technologies to effectively use the large amount of invested computing resources. To improve overall performance, tasks must be allocated to appropriate agents, and from this viewpoint, a number of negotiation protocols were proposed in the MAS context. Most assume a small-scale, unbusy environment, however. We previously reported the possibility that, using contract net protocol (CNP), the overall efficiency improved by an adequate control of degree of fluctuation in the awarding phase, when the MMAS is in specific states. In this paper, we propose the method to estimate these specific states from the bid values, which have hitherto not been used effectively. Then the new manager-side policy flexibly and autonomously introduces some degree of fluctuation responsive to the estimated states. We also demonstrate that our proposed CNP policy provides considerably better performance than naive CNP and CNP with inflexible policies, even though our policy does not use global information.