It is intended to provide a novel fluorescent protein originating in an organism other than Aequorea coerulescens. Thus, a fluorescent protein originating in Galaxea fascicularis which has the following characteristics is provided: (1) having an average molecular weight of about 27000; (2) forming a tetramer in the equilibrated state; (3) showing the maximum excitation wavelength of 492 nm and the maximum fluorescent wavelength of 505 nm; (4) showing a molar absorbance index of 74100; (5) showing a quantum yield of 0.625; and (6) having a low pH-sensitivity of the fluorescent properties within a pH range of 5 to 12.
