A plastic wavelength shifting fiber includes a core containing a fluorescent agent having a peak of a fluorescence spectrum in a wavelength range of 450 to 550 nm, and a cladding covering an outer peripheral surface of the core and has a refractive index lower than that of the core. A sum of the number of carbon and oxygen atoms of the fluorescent agent is 10 to 25, and a quantum yield QE of the fluorescent agent and an overlap parameter OL thereof defined by Formula (2) satisfy Formula (1):

OL×(1−QE)