  We have carried out the observations of the OMC-2 FIR 3/4 region with the NMA
and ASTE in the H$^{13}$CO$^{+}$ (1--0), $^{12}$CO (3--2, 1--0), SiO ($v$=0,
$J$=2--1), CS (2--1), and CH$_3$OH ($J_K$=7$_K$--6$_K$) lines and in the 3.3 mm
continuum emission. Our NMA observations in the H$^{13}$CO$^{+}$ emission have
revealed 0.07 pc-scale dense gas associated with FIR 4. The $^{12}$CO
(3--2,1--0) emission shows high-velocity blue and red shifted components at the
both north-east and south-west of FIR 3, suggesting a molecular outflow nearly
along the plane of the sky driven by FIR 3. The SiO and the CH$_{3}$OH emission
are detected around the interface between the outflow and the dense gas.
Furthermore, the $^{12}$CO (1--0) emission shows an L-shaped structure in the
P-V diagram. These results imply presence of the shock due to the interaction
between the molecular outflow driven by FIR 3 and the dense gas associated with
FIR 4. Moreover, our high angular-resolution observations of FIR 4 in the 3.3
mm continuum emission have first found that FIR 4 consists of eleven dusty
cores. The separation among these cores is on the same order of the Jeans
length, suggesting that the fragmentation into these cores has been caused by
the gravitational instability. The time scale of the fragmentation is similar
to the time scale of the interaction between the molecular outflow and the
dense gas. We suggest that the interaction between the molecular outflow from
FIR 3 and the dense gas associated with FIR 4 triggered the fragmentation into
these dusty cores, and hence the next generation the cluster formation.
