The present invention relates to a phosphor represented by the following general formula (I), comprising: a composite oxide containing a divalent and trivalent metal elements as a host crystal; and at least Ce as an activator element in said host crystal, wherein the phosphor has a maximum emission peak in a wavelength range of from 485 nm to 555 nm in the emission spectrum at room temperature: M1aM2bM3cOd  (I) wherein M1 represents an activator element containing at least Ce; M2 represents a divalent metal element; M3 represents a trivalent metal element; a is a number within a range of 0.0001≦a≦0.2; b is a number within a range of 0.8≦b≦1.2; c is a number within a range of 1.6≦c≦2.4; and d is a number within a range of 3.2≦d≦4.8. Further, a light emitting device comprising said phosphor and a display and a lighting system having said light emitting device as a light source are disclosed. In accordance with the present invention, a phosphor which can be easily produced and can provide a light emitting device having a high color rendering, a light emitting device comprising the phosphor, and a display and a lighting system comprising the light emitting device as a light source can be provided.