The objective of this study is to analyze and to characterize the regional forecast error of hourly PV power generation in Japan. To make the analysis, data of 517 PV systems installed in 5 regions in Honshu Island were used to make 1 year of hourly forecasts. The regional forecasts of PV power were obtained from individual forecasts of the systems regarded in the study. Such forecasts were done using support vector regression and weather related information. The results showed that typical RMSE normalized by the region installed capacity were between 0.059 and 0.069kWh/kW_cap. Values for the mean absolute error were near 60% of the RMSE being between 0.036 and 0.043kWh/kW_cap. Furthermore, the smoothing effect was also characterized and values of 30% to 45% of error reduction were obtained according to the region and its PV systems characteristics. The study also provided values for the seasonal regional error in the Honshu Island, and it constitutes an important effort in the characterization of the regional forecast error of PV power generation in Japan.