String matching circuits have been studied extensively for Intrusion Detection Systems so far. An NFA-based string matching circuit, one of the works, has expandability of processing data width. However the resource requirement increases markedly, it was difficult to implement an NFAbased string matching circuit with whole the Snort 2.3.3 rule (35461 characters) that processes at 10 Gbps on a single FPGA. In this paper, we propose a highly efficient string matching circuit for FPGA. In our circuit, redundant ANDgates and states in the NFA are eliminated to reduce the resource requirement. Consequently, our circuit is reduced in the resources requirement by over 50% as compared with a previous NFA-based circuit, and the synthesis result shows that a string matching circuit that includes the whole Snort 2.3.3 rule can be implemented onto a single xc2vp-100-6 FPGA with throughput over 10 Gbps.