This paper proposes a method using partial reconfiguration to realize a compact regular expression matching engine, which can update a pattern quickly. In the proposed method, a set of partial circuits, each of which handles a different class of regular expressions, are provided in advance. When a regular expression pattern is given, a compact matching engine dedicated to the pattern is implemented on FPGA by combining the partial circuits according to the given pattern using partial reconfiguration. The method can update a pattern quickly, since it does not need re-design of a circuit. Experimental results show that the proposed method reduces 60% circuit size compared with the previous method without increasing the pattern updating time significantly.