In mobile ad hoc networks (MANET), reputation systems and price-based systems have been proposed. These systems require management systems for trust and reward. Due to the characteristics of MANET, the management systems are required to securely manage reputation and reward in a distributed manner. In this paper, we propose a Distributed Management system for Trust and Reward in MANET, called DMTR. DMTR can effectively detect uncooperative nodes which drop packets illegally. DMTR is utilising a blockchain which is a technique to manage virtual credit in peer-to-peer (P2P) networks. DMTR sets 'mining nodes' which play a role of managing the blockchain and introduces cooperative mining to accelerate settlement speed while keeping security. We confirm the efficiency of DMTR in network performances by simulation.