In ad hoc networks where mobile nodes form networks autonomously, many unidirectional links can be generated due to the diversity of transmission range of each node In order to achieve high connectivity in such networks, routing protocols should construct routes by aggressively using unidirectional links. Typical existing routing protocols such as DSR(Dynamic Source Routing) are basically designed assuming links are bidirectional, and they generate substantial control traffic in the unidirectional routing since their optimization schemes are not effective for unidirectional links. This paper presents a novel on-demand ad hoc routing method called FOCUS (controlled-Flooding-based ad hoc routing protocol using Overheard hop Count information to support Unidirectional linkS). FOCUS reduces control traffic of route reconstruction as compared with conventional method by issuing route request in the restricted region around the broken route. The results of performance evaluation by simulation show FOCUS reduces the number of RREQ(Route REQuest) packets by about 60 % and reduces packet transmission delay by about 30% compared to DSR.