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Active solar-type stars show large quasi-periodic brightness variationscaused by stellar rotations with star spots, and the amplitude changes as thespots emerge and decay. The Kepler data are suitable for investigations on theemergence and decay processes of star spots, which are important to understandunderlying stellar dynamo and stellar flares. In this study, we measuredtemporal evolutions of star spot area with Kepler data by tracing local minimaof the light curves. In this analysis, we extracted temporal evolutions of starspots showing clear emergence and decay without being disturbed by stellardifferential rotations. We applied this method to 5356 active solar-type starsobserved by Kepler and obtained temporal evolutions of 56 individual starspots. We calculated lifetimes, emergence and decay rates of the star spotsfrom the obtained temporal evolutions of spot area. As a result, we found thatlifetimes ($T$) of star spots are ranging from 10 to 350 days when spot areas($A$) are 0.1-2.3 percent of the solar hemisphere. We also compared them withsunspot lifetimes, and found that the lifetimes of star spots are much shorterthan those extrapolated from an empirical relation of sunspots ($T\propto A$),while being consistent with other researches on star spot lifetimes. Theemerging and decay rates of star spots are typically $5 \times 10^{20}$ $\rmMx\cdot h^{-1}$ ($8$ $\rm MSH\cdot h^{-1}$) with the area of 0.1-2.3 percent ofthe solar hemisphere and are mostly consistent with those expected fromsunspots, which may indicate the same underlying processes.

Lifetimes and Emergence/Decay Rates of Star Spots on Solar-type Stars Estimated by Kepler Data in Comparison with Those of Sunspots