  We present measurements of the rates of high-redshift Type Ia supernovae
derived from the Subaru/XMM-Newton Deep Survey (SXDS). We carried out repeat
deep imaging observations with Suprime-Cam on the Subaru Telescope, and
detected 1040 variable objects over 0.918 deg$^2$ in the Subaru/XMM-Newton Deep
Field. From the imaging observations, light curves in the observed $i'$-band
are constructed for all objects, and we fit the observed light curves with
template light curves. Out of the 1040 variable objects detected by the SXDS,
39 objects over the redshift range $0.2 < z < 1.4$ are classified as Type Ia
supernovae using the light curves. These are among the most distant SN Ia rate
measurements to date. We find that the Type Ia supernova rate increase up to $z
\sim 0.8$ and may then flatten at higher redshift. The rates can be fitted by a
simple power law, $r_V(z)=r_0(1+z)^\alpha$ with
$r_0=0.20^{+0.52}_{-0.16}$(stat.)$^{+0.26}_{-0.07}$(syst.)$\times 10^{-4} {\rm
yr}^{-1}{\rm Mpc}^{-3}$, and
$\alpha=2.04^{+1.84}_{-1.96}$(stat.)$^{+2.11}_{-0.86}$(syst.).
