Let $μ ∈ 𝓐 (ℝ^{d})'$ be an analytic functional and let $T_μ$ be the corresponding convolution operator on Sato's space $𝓑 (ℝ^{d})$ of hyperfunctions. We show that $T_μ$ is surjective iff $T_μ$ admits an elementary solution in $𝓑 (ℝ^{d})$ iff the Fourier transform μ̂ satisfies Kawai's slowly decreasing condition (S). We also show that there are $0 ≠ μ ∈ 𝓐 (ℝ^{d})'$ such that $T_μ$ is not surjective on $𝓑 (ℝ^{d})$.