  We consider the wave propagating in the Einstein & de Sitter spacetime. The
covariant d'Alembert's operator in the Einstein & de Sitter spacetime belongs
to the family of the non-Fuchsian partial differential operators. We introduce
the initial value problem for this equation and give the explicit
representation formulas for the solutions. We also show the $L^p - L^q$
estimates for solutions.
