  Current sheet is a common structure involved in solar eruptions. However, it
is observed in minority of the events and the physical properties of its fine
structures during a solar eruption are rarely investigated. Here, we report an
on-disk observation that displays 108 compact, circular or elliptic bright
structures, presumably plasma blobs, propagating bidirectionally along a flare
current sheet during a period of $\sim$24 minutes. From extreme ultraviolet
images, we have investigated the temporal variation of the blob number around
the flare peak time. The current sheet connects the flare loops and the
erupting filament. The width, duration, projected velocity, temperature, and
density of these blobs are $\sim$1.7$\pm$0.5\,Mm, $\sim$79$\pm$57\,s,
$\sim$191$\pm$81\,\kms, $\sim$10$^{6.4\pm0.1}$ K, and $\sim$10$^{10.1\pm0.3}$
cm$^{-3}$, respectively. The reconnection site rises with a velocity of
$\leqslant$69\,\kms. The observational results suggest that plasmoid
instability plays an important role in the energy release process of solar
eruptions.
