An earthquake swarm occurred under the Hida Mountains in central Japan in 1998. The focal area, which expanded from south to north, was distributed above the low-velocity and high-attenuation zone, which lies under the main range. During the swarm, there was a migration of focal areas with time delays. In this paper, we investigate the spatiotemporal distribution of earthquakes in the swarm and discuss the phenomenon that must have controlled the seismicity. Understanding the complicated spatial pattern of seismicity, we investigate the dependency of the occurrence of earthquakes on the static stress changes caused by preceding earthquakes. Our findings show that, for each of 18 major earthquakes (magnitudes 4.0 or higher), the estimated distribution of the resulting Coulomb failure stress corresponds to the expansion of focal areas and the distribution of the seismically quiescent region. However, the detailed structure of seismicity cannot be explained only by the static stress changes. We discuss two additional factors which may control delayed fractures: flow of underground water for the seismicity around the southernmost focal cluster and stress corrosion process for the leaps of seismicities. The results of this study suggest that the 1998 Hida swarm was strongly affected by the disturbances of a static stress field that was created by the swarm itself, although the magnitudes of static stress change are small. The seismic activity was initiated by swarm-type seismicity around the southernmost cluster and then expanded northward gradually due to the increase in static stress.