The final results of a nationwide indoor radon survey are presented based on one year measurements at more than 7, 000 houses throughout Japan. In conclusion, the annual average indoor radon concentrations in 5, 717 houses are finally obtained as the output of the survey after scrutinizing the raw data of more than 28, 000 measurements. The arithmetic mean and its standard deviation of radon concentration are given to be 20.8 and 18.8Bqm^-3, respectively. The median, 90 percentile and 99.5 percentile were 16.0, 35.5 and 138Bqm^-3, respectively. The arithmetic mean, median and 90 percentile of each prefecture are also presented to identify the regional variation of radon concentrations. Radon concentrations in wooden houses show regional differences closely related to granite distribution. However, radon concentrations in non-wooden houses show no typical pattern related to geology. The equivalent dose due to radon progeny in Japan is estimated to be 0.59mSvy^-1 applying the same assumptions given in the UNSCEAR 1993 Report to the arithmetic mean obtained in this survey.