It is intended to provide novel fluorescent proteins originating in an organism other than <i>Aequorea coerulescens</i>. Namely, a fluorescent protein originating in <i>Fungia sp</i>. which has the following characteristics: (1) showing a maximum excitation wavelength of 455 nm and a maximum fluorescent wavelength of 488 nm; (2) showing a molar absorptivity at 455 nm of from 38700 or 27700; (3) showing a quantum yield of 0.85 or 0.81; and (4) showing a stable pH sensitivity of the fluorescent characteristics at pH 5 to 9. Another fluorescent protein originating in <i>Fungia sp</i>. which has the following characteristics: (1) showing a maximum excitation wavelength of 548 nm and a maximum fluorescent wavelength of 561 nm; (2) showing a molar absorptivity at 548 nm of from 75900 or 51000; (3) showing a quantum yield of 0.44 or 0.50; (4) showing a pH sensitivity of the fluorescent characteristics of pKa<5.0.
