As calcium indicator protein having excellent fluorescence properties and calcium reactive calcium calmodulin dependent protein kinase kinase calmodulin binding sequence (Ckkap sequence) encoding the calcium binding sequence of nucleotides and calmodulin encoding (CaM sequence) to one of the nucleotides of the nucleotide There 'end side, the other nucleotides are 3 nucleotides that encode the fluorescent protein 5' nucleotides encoding the fluorescent protein to provide a DNA which is attached to the terminal side. Calcium indicator protein encoded by this DNA, by having ckkap sequence as a binding domain for CaM sequence calcium is bound, exhibits excellent fluorescent properties and calcium reactivity compared with the conventional calcium indicator protein.