The present invention provides a red-emitting phosphor emitting luminescence of excellent color purity with high efficiency under the excitation with near UV light, and it also provides a color image displaying device employing that phosphor. This phosphor comprises an ARS2 matrix (A is at least one of Na, K and Rb, and R is at least one of Y, Gd and Lu) doped with 0.003 to 0.3 mol % of Bi and 0.1 to 3 mol % of Mn, and is suitable as a red-emitting phosphor used in a color image displaying device without a color filter.