  We report the detection of an H-alpha emission line in the low resolution
spectrum of a quasar, RX J1759.4+6638, at a redshift of 4.3 with the InfraRed
Camera (IRC) onboard the AKARI. This is the first spectroscopic detection of an
H-alpha emission line in a quasar beyond z=4. The overall spectral energy
distribution (SED) of RX J1759.4+6638 in the near- and mid-infrared wavelengths
agrees with a median SED of the nearby quasars and the flux ratio of
F(Ly-alpha)/F(H-alpha) is consistent with those of previous reports for
lower-redshift quasars.
