The antiperovskite (inverse perovskite) oxides are charge-inverted analogues of the ordinary perovskite oxides. In this article, we explain our recent discovery of superconductivity in Sr(3-x)SnO, the first superconductor among the antiperovskite oxides. The pristine compound without Sr deficiency is a candidate of the Dirac semimetal. We found that the Sr-deficient compound exhibits superconductivity with the critical temperature of around 5 K, due to doped hole carriers. Theoretically, it is proposed that the strong mixing of d and p orbitals in the valence band can lead to topological superconductivity in Sr(3-x)SnO.