The temporal variation of multifractal properties in spatial distribution of seismicity in the region affected by the main shock of the Western Tottori Prefecture, Japan, earthquake of October 6, 2000 (M = 7.3) and its aftershock sequence are investigated. We use earthquake catalog data from 1985 to 2001 in order to understand the process and mechanism preceding a large, shallow earthquake. A monotonous decrease of multifractal dimension Dq with a wide range of q appeared clearly for about two years prior to this large, shallow earthquake; Dq then increased to a maximum at the time of the main shock. During the aftershock sequence, Dq oscillated between 2.0 and 0.7. The decrease and then increase of Dq with respect to the spatial distribution of seismic events indicate clustering and declustering in multifractal structure, respectively. The temporal variation of Dq reflects the accumulation and release of strain energy within the tectonic stress field.