  Time evolution of a black hole lattice universe with a positive cosmological
constant $\Lambda$ is simulated. The vacuum Einstein equations are numerically
solved in a cubic box with a black hole in the center. Periodic boundary
conditions on all pairs of opposite faces are imposed. Configurations of
marginally trapped surfaces are analyzed. We describe the time evolution of not
only black hole horizons, but also cosmological horizons. Defining the
effective scale factor by using the area of a surface of the cubic box, we
compare it with that in the spatially flat dust dominated FLRW universe with
the same value of $\Lambda$. It is found that the behaviour of the effective
scale factor is well approximated by that in the FLRW universe. Our result
suggests that local inhomogeneities do not significantly affect the global
expansion law of the universe irrespective of the value of $\Lambda$.
