We investigated regional dependence of the slope of the initial part of P-wave envelope, which is used to determine epicentral distances in the Japan Meteorological Agency and Japan Railway Company earthquake early warning (EEW) systems. The Tohoku region was chosen as the study region. We retrieved 19,899 strong motion borehole data for 265 events with magnitudes in the range from 5.0 to 7.6 from KiK-net (Kiban Kyoshin network). Following previous studies, we fitted the function to the initial part of P-wave envelopes to obtain sets of the parameters of A and B and obtained the following relation by the least squares method. This is consistent with the previous study which used the data set similar to that of this study within one standard deviation. Then, we determined intercepts of the above formula for each event keeping the slope to -2.27 to investigate the regional dependence. There appear two tendencies; shallow crust events have lower values of c, and deeper events in the subducting slab have higher values of c. We examined the B values obtained for the same set of the stations for the selected three events, and found that their differences are significant. These results suggest that the differences of the coefficient c are likely to be due to earthquake characteristics.