The present invention provides an oxide phosphor for use in an electroluminescent device, which phosphor is capable of providing a high-luminance EL device while the composition thereof is controlled to be as simple as possible, and which phosphor attains multi-color and full-color light emissions without the need for treatment at a high temperature greatly in excess of 1,000° C. The invention also provides an electroluminescent device employing the phosphor. The oxide phosphor for use in an electroluminescent device is formed from an yttrium (Y) oxide as a matrix and at least one transition metal element as an activator, or from a Y—Ge—O oxide or a Y—Ge—Si—O oxide as a matrix and at least one metallic element, as a luminescence center, selected from among transition metal elements and rare earth metal elements.