Radar/Raingauge-Analyzed Precipitation (RA) represents 1 km-grid precipitation after 2006 created by combining radar precipitation and ground precipitation, i.e., Automated Meteorological Data Acquisition System (AMeDAS) of Japan Meteorological Agency along with ground data observed by other organizations. Although RA is slightly greater than ground precipitation, no earlier studies investigated the spatial distribution of this accuracy across Japan using 1 km grid data, as clarified in this study. We selected hourly data of RA and AMeDAS located closest each other, for which miss rates were less than 10% in 2006-2010. We then investigated the distribution of the annual precipitation ratio (RA/AMeDAS). The ratio diverged in the smaller annual precipitation, but converged to ca. 1.2 for larger annual precipitation. By setting the observational area of 46 radars across Japan using Thiessen method, we investigated the relation between the annual precipitation ratio and the distance from the radar to AMeDAS station. We found only negative relation was statistically significant. As a possible reason for this relation, we considered that RA far from the radar is affected by the attenuating and shadowing effect of heavy rainfall near the radar.