Recent space-based observations (e.g., Kepler mission) found thousands of ``superflares’’ on G-, K-, and M-type stars. These superflare stars show quasi-periodic brightness variations caused by the rotation of the star with starspots. We analyzed the statistical properties of starspots on G-, K-, and M-type stars and their correlation with the flare activity. The analysis shows that the fraction of stars showing large-amplitude rotational variations, which are thought to be the signature of the large starspots, decreases as the rotation period increases. We found that there is a good correlation between the bolometric energy of the largest superflares and area of starspots estimated from the amplitude of rotational light variations. The bolometric energy released by the largest flare on the star is consistent with the magnetic energy stored near the starspots. We also found that the frequency of superflares correlates with the starspot area. The average frequency of flares with a given bolometric energy is roughly proportional to the area of starspots. Our results suggest that flare activity level (e.g., energy of the largest flares, occurrence frequency) of the late-type stars can be determined by the area of starspots.

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