  We report the results of H13CO+(1-0), CO(1-0), and 3.3 mm dust continuum
observations toward one of the strongest mm-wave sources in OMC-3, MMS 7, with
the Nobeyama Millimeter Array (NMA) and the Nobeyama 45 m telescope. With the
NMA, we detected centrally-condensed 3.3 mm dust-continuum emission which
coincides with the MIR source and the free-free jet. Our combined H13CO+
observations have revealed a disk-like envelope. The size and the mass of the
disk-like envelope are 0.15 times 0.11 pc and 5.1 - 9.1 M_sun, respectively.
The combined map also shows that the outer portion of the disk-like envelope
has a fan-shaped structure which delineates the rim of the CO(1-0) outflow
observed with the NMA. The position-velocity (P-V) diagrams in the H13CO+ (1-0)
emission show that the velocity field in the disk-like envelope is composed of
a dispersing gas motion and a possible rigid-like rotation. The mass dispersing
rate is estimated to be (3.4 - 6.0) times 10^-5 M_sun/yr, which implies that
MMS 7 has an ability to disperse ~10 M_sun during the protostellar evolutional
time of a few times 10^5 yr. The specific angular momentum of the possible
rotation in the disk-like envelope is nearly two orders of magnitude larger
than that in low-mass cores. The turn-over point of the power law of the
angular momentum distribution in the disk-like envelope (< 0.007 pc), which is
likely to be related to the outer radius of the central mass accretion, is
similar to the size of the 3.3 mm dust condensation. The intermediate-mass
protostar MMS 7 is in the last stage of the main accretion phase and that the
substantial portion of the outer gas has already been dispersed, while the mass
accretion may still be on-going at the innermost region traced by the dusty
condensation.
