  From neutron diffraction measurements on a quasi-1D Ising-like Co$^{\rm 2+}$
spin compound BaCo$_{\rm 2}$V$_{\rm 2}$O$_{\rm 8}$, we observed an appearance
of a novel type of incommensurate ordering in magnetic fields. This ordering is
essentially different from the N{\' e}el-type ordering, which is expected for
the classical system, and is caused by quantum fluctuation inherent in the
quantum spin chain. A Tomonaga-Luttinger liquid (TLL) nature characteristic of
the gapless quantum 1D system is responsible for the realization of the
incommensurate ordering.
