The purpose of this study is to analyze the horizontal inter-organizational network among competitors, which is invisible networks in the management of firms in the regional industry, by means of social network analysis and to clarify those structure and mechanism. The subject of this studyʼs analysis is the katsuobushi (dried bonito) production industry in Makurazaki City, Kagoshima Prefecture. The analysis showed that the horizontal inter-organizational networks among katsuobushi manufacturers in Makurazaki were networks structure and mechanism with good information sharing and circularity. These networks have the ability to deal with uncertainty and the effect of reducing transaction costs as management resources for firms.