We report a superconducting transition in a LaO epitaxial thin film with the superconducting transition onset temperature (T-c) at around 5 K. This T-c is higher than those of other lanthanum monochalcogenides and opposite to their chemical trend: T-c = 0.84, 1.02, and 1.48 K for LaX (X = S, Se, Te), respectively. The carrier control resulted in a dome-shaped Tc as a function of electron carrier density. In addition, the T-c was significantly sensitive to epitaxial strain in spite of the highly symmetric crystal structure. This rock-salt superconducting LaO could be a building block to design novel superlattice superconductors.