We focused on the regionality of crustal thickness and examined the differences in the scaling relationship between the seismic moment and rupture area for crustal earthquakes. We found good agreement between the scaling relationships and earthquake data when the saturated rupture width and stress drop was set to 16 km and 3.1 MPa, respectively, in regions with a relatively thin crust, including Japan, and set to 28 km and 2.0 MPa, respectively, in regions with a relatively thick crust. For crustal earthquakes, the accuracy of the scaling relationship is improved by considering the crustal thickness.