  We consider Kaku theory as introduced in M. Kaku, Phys. Lett. B 200, 22
(1988) and investigate classical solutions. In particular, we obtain that the
equation of motion with the restriction $k_-=0$ in the Kaku theory is
equivalent to the equation of motion in Witten theory. Because of this
property, some solutions including the tachyon vacuum solution in the Witten
theory satisfy also the equation of motion in the Kaku theory. In addition, we
confirm that the cohomology around the tachyon vacuum solution is trivial also
in the Kaku theory.
