We examined several previously proposed models of the process by which large intraplate earthquakes are generated, and found the most plausible to be the ‘localized shear model,’ in which seismogenic faults have downward extensions in the lower crust and the localized shear deformation on the downward extensions accumulate stress on the seismogenic faults. Further, localized shear deformation may accelerate before a large intraplate earthquake occurs. This model can explain various phenomena related to crustal deformation in the Japanese Islands: preslips, seismicity, distribution of active faults, and stress and strain state. It will play an important role in the forecasting and prediction of large intraplate earthquakes.