In recent years, applications such as Intelligent Transportation System, Cyber-physical System, Wireless Sensor Networks, are deployed especially in urban areas, where the broadband mobile communication system is well developed, so the variety of applications running on ad-hoc networks tends to increase in future. Therefore, the demand of the interconnection of HANETs (heterogeneous ad-hoc networks) becomes growing. Moreover, because the communication entity is changing from humans to things, the communication delay that the network infrastructure should guarantee has been becoming stricter. In this paper, assuming a situation in which HANETs are directly interconnected by some protocol translators (called gateways, or GWs), we propose an optimum GW placement algorithm to maximize the allowable delay satisfaction rate under the assumption that each flow in the networks has an individual constraint of allowable delay. We evaluate our proposed method using a computer simulation. We also consider the impact of link disruption prediction for the performance improvement.