  We conducted the time-resolved simultaneous optical spectroscopic and
photometric observations of mid M dwarf flare stars YZ CMi, EV Lac, and AD Leo.
Spectroscopic observations were obtained using Apache Point Observatory 3.5m
and Small \& Moderate Aperture Research Telescope System 1.5m telescopes during
31 nights. Among the 41 detected flares, seven flares showed clear blue wing
asymmetries in the H$\alpha$ line, with various correspondences in flare
properties. The duration of the blue wing asymmetries range from 20 min to 2.5
hours, including a flare showing the shift from blue to red wing asymmetry.
Blue wing asymmetries can be observed during both white-light and candidate non
white-light flares. All of the seven flares showed blue wing asymmetries also
in the H$\beta$ line, but there are large varieties on which other
chromospheric lines showed blue wing asymmetries. One among the 7 flares was
also observed with soft X-ray spectroscopy, which enabled us to estimate the
flare magnetic field and length of the flare loop. The line-of-sight velocities
of the blue-shifted components range from -73 to -122 km s$^{-1}$. Assuming
that the blue-shifts were caused by prominence eruptions, the mass of upward
moving plasma was estimated to be 10$^{15}$ -- 10$^{19}$ g, which are roughly
on the relation between flare energy and erupting mass expected from solar
coronal mass ejections (CMEs). Although further investigations are necessary
for understanding the observed various properties, these possible prominence
eruptions on M-dwarfs could evolve into CMEs, assuming the similar acceleration
mechanism with solar eruptions.
