To provide a chemiluminescent reagent emitting light having a long wavelength and a high light emission intensity by being reacted with superoxide anions.

Imidazo[1,2-a]pyrazine-3-ones or the like emitting light by being reacted with superoxide anions and a fluorescent pigment are bonded together through a spacer. As for the fluorescent pigment, rhodamines are selected as a pigment whose excitation spectrum is overlapped with an emission spectrum of the imidazo[1,2-a]pyrazine-3-ones, to thereby perform smooth light emission energy resonance movement.