A phosphor and a light emitting device including the phosphor may be provided that emits light having a peak wavelength between a green wavelength band and a yellow wavelength band and has a triclinic system crystal structure of which the chemical formula is MSi2N2O2, M=CaxSryEuz(x+y+z=1), wherein, when three sides of a unit crystal lattice of the crystal structure are a, b and c and corner angles are α, β and γ, the crystal structure has relationships of a≠b≠c and α≠β≠γ, and wherein, in a, b and c, any one of them is more than twice as much as one of the other two, and the values of the other two are so similar that they do not exceed the double of each.