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We study the comoving space density of X-ray-selected luminous activegalactic nuclei (AGNs) and the obscured AGN fraction at high redshifts ($3 < z< 5$) in the Subaru/{\it XMM-Newton} Deep Survey (SXDS) field. From an X-raysource catalog with high completeness of optical identification thanks to deepoptical images, we select a sample of 30 AGNs at $z > 3$ with intrinsic(de-absorbed and rest-frame 2--10 keV) luminosities of $L_{\rm X} = 10^{44-45}$erg s$^{-1}$ detected in the 0.5--2 keV band, consisting of 20 and 10 objectswith spectroscopic and photometric redshifts, respectively. Utilizing the$1/V_{\rm max}$ method, we confirm that the comoving space density of luminousAGNs decreases with redshift above $z > 3$. When combined with the {\itChandra}-COSMOS result of Civano et al.\ (2011), the density decline of AGNswith $L_{\rm X} = 10^{44-45}$ erg s$^{-1}$ is well represented by a power lawof $(1 + z)^{-6.2 \pm 0.9}$. We also determine the fraction of X-ray obscuredAGNs with $N_{\rm H} > 10^{22}$ cm$^{-2}$ in the Compton-thin population to be0.54$^{+0.17}_{-0.19}$, by carefully taking into account observational biasesincluding the effects of photon statistics for each source. This result isconsistent with an independent determination of the type-2 AGN fraction basedon optical properties, for which the fraction is found to be 0.59$\pm$0.09.Comparing our result with that obtained in the local Universe, we conclude thatthe obscured fraction of luminous AGNs increases significantly from $z=0$ to$z>3$ by a factor of 2.5$\pm$1.1.

Comoving Space Density and Obscured Fraction of High-Redshift Active Galactic Nuclei in the Subaru/{\it XMM-Newton} Deep Survey