Provided are a scintillator and a scintillator plate fitted with the scintillator exhibiting high emission luminance even though a heat treatment temperature of CsI columnar crystals is high, and also capable of exhibiting high emission luminance since these crystals can be formed on each of various kinds of evaporation substrates. Also disclosed is a scintillator comprising columnar crystals formed via vapor deposition of cesium iodide and an additive comprising a thallium compound, wherein the thallium compound has a melting point of 400-700° C., and has a molecular weight of 206-300.