We present results of our large area survey for z'-band dropout galaxies at z= 7 in a 1568 arcmin 2 sky area covering the SDF and GOODS-N fields. Combining our ultra-deep Subaru/Suprime-Cam z'-and y-band (λ eff= 1 μm) images with legacy data of Subaru and Hubble Space Telescope, we have identified 22 bright z-dropout galaxies down to y= 26, one of which has a spectroscopic redshift of z= 6.96 determined from Lyα emission. The z= 7 luminosity function yields the best-fit Schechter parameters of ϕ*= 0.69+ 2.62− 0.55× 10− 3 Mpc− 3, M* UV=− 20.10±0.76 mag, and α=− 1.72±0.65, and indicates a decrease from z= 6 at a> 95% confidence level. This decrease is beyond the cosmic variance in our two fields, which is estimated to be a factor of≲ 2. We have found that the cosmic star formation rate density drops from the peak at z= 2–3 to z= 7 roughly by a factor of∼ 10 but not larger than∼ 100. A comparison with the reionization models suggests either that the universe could not be totally ionized by only galaxies at z= 7, or more likely that properties of galaxies at z= 7 are different from those at low redshifts having, eg, a larger escape fraction (≳ 0.2), a lower metallicity, and/or a flatter initial mass function. Our SDF z-dropout galaxies appear to form 60 Mpc long filamentary structures, and the z= 6.96 galaxy with Lyα emission is located at the center of an overdense region consisting of four UV bright dropout candidates, which might suggest an existence of a well-developed ionized bubble at z= 7.