  We report high precision transit photometry of GJ1214b in JHKs bands taken
simultaneously with the SIRIUS camera on the IRSF 1.4m telescope at Sutherland,
South Africa. Our MCMC analyses show that the observed planet-to-star radius
ratios in JHKs bands are R_{\rm p}/R_{\rm s,J} = 0.11833 \pm 0.00077, R_{\rm
p}/R_{\rm s,H} = 0.11522 \pm 0.00079, R_{\rm p}/R_{\rm s,Ks} = 0.11459 \pm
0.00099, respectively. The radius ratios are well consistent with the previous
studies by Bean et al. (2011) within 1\sigma, while our result in Ks band is
shallower than and inconsistent at 4\sigma\ level with the previous
measurements in the same band by Croll et al. (2011). We have no good
explanation for this discrepancy at this point. Our overall results support a
flat transmission spectrum in the observed bands, which can be explained by a
water-dominated atmosphere or an atmosphere with extensive high-altitude clouds
or haze. To solve the discrepancy of the radius ratios and to discriminate a
definitive atmosphere model for GJ1214b in the future, further transit
observations around Ks band would be especially important.
