  Transition metal dichalcogenides with superperiodic lattice distortions have
been widely investigated as the platform of ultrafast structural phase
manipulations. Here we performed ultrafast electron diffraction on
room-temperature TaTe$_2$, which exhibits peculiar double zigzag chain pattern
of Ta atoms. From the time-dependent electron diffraction pattern, we revealed
a photoinduced change in the crystal structure occurring within <0.5 ps, though
there is no corresponding high-temperature equilibrium phase. We further
clarified the slower response (~1.5 ps) reflecting the lattice thermalization.
Our result suggests the unusual ultrafast crystal structure dynamics specific
to the non-equilibrium transient process in TaTe$_2$.
