  We report on the elemental abundances of the carbon-enhanced metal-poor
(CEMP) star J2217+2104 discovered by our metal-poor star survey with LAMOST and
Subaru. This object is a red giant having extremely low Fe abundance
([Fe/H]=-4.0) and very large enhancement of C, N, and O with excesses of Na,
Mg, Al, and Si. This star is a new example of a small group of such CEMP stars
identified by previous studies. We find a very similar abundance pattern for
O-Zn in this class of objects that shows enhancement of elements up to Si and
normal abundance of Ca and Fe-group elements. Whereas the C/N ratio is
different among these stars, the (C+N)/O ratio is similar. This suggests that C
was also yielded with similar abundance ratios relative to O-Zn in progenitors,
and was later affected by the CN-cycle. By contrast, the heavy neutron-capture
elements Sr and Ba are deficient in J2217+2104, compared to the four objects in
this class previously studied. This indicates that the neutron-capture process
in the early Galaxy, presumably the r-process, has no direct connection to the
phenomenon that has formed such CEMP stars. Comparisons of the abundance
pattern well determined for such CEMP stars with those of supernova
nucleosynthesis models constrain the progenitor mass to be about 25Msun, which
is not particularly different from typical mass of progenitors expected for
extremely metal-poor stars in general.
