  We investigate the planetary transit detectability in the presence of stellar
rotational activity from light curves for young M-dwarfs and estimate
improvements of the detection at near-infrared (NIR) wavelengths. Making maps
of the transit signal detection efficiency over the orbital period and
planetary radius with light curves of members of four clusters, Hyades,
Praesepe, Pleiades, and Upper Scorpius observed by the K2 mission, we evaluate
the detectability for the rotation period and modulation semi-amplitude. We
find that the detection efficiency remarkably decreases to about 20% for
rapidly rotators with P_{rot} <= 1 d and the lack of planets in Pleiades is
likely due to the high fraction of rapidly rotating M-dwarfs. We also evaluate
the improvements of the planet detection with NIR photometry via tests using
mock light curves assuming that the signal amplitude of stellar rotation
decreases at NIR wavelengths. Our results suggest that NIR photometric
monitoring would double relative detection efficiency for transiting planetary
candidates with P_{rot} <= 1 d and find planets around M-dwarfs with
approximately 100 Myr missing in the past transit surveys from the space.
