A plastic glass optical fiber comprising: a glass core composed of glass; a polymer core composed of fluorine addition polymer, which is disposed around a periphery of the glass core, and has a refractive index lower than a refractive index of the glass core; and a polymer cladding composed of polymer, which is disposed around a periphery of the polymer core, and has a refractive index lower than the refractive index of the polymer core, wherein the plastic glass optical fiber satisfies following relations: a diameter a1 of the glass core is within a range between 110 μm or more and 200 μm or less, and when a diameter of the glass core is set to be a1 and a diameter of the polymer core is set to be a2, a parameter X defined as X = a2 2 /a1 2 is within a range of 1.15 ≤ X ≤ 2.9; and when a relative refractive index difference between the glass core and the polymer core is set to be Δ1 and a relative refractive index difference between the polymer core and the polymer cladding is set to be Δ2, a parameter Y defined as Y = Δ2/Δ1 is within a range of 0.25 ≤ Y ≤ 0.84X - 0.68 when the parameter X is within a range of 1.15 ≤ X ≤ 2, and the parameter Y is within a range of 0.48X - 0.71 ≤ Y ≤ - (2/9)X + 13/9 when the parameter X is within a range of 2 ≤ X ≤ 2.9; and when the diameter of the polymer core is set to be a2, the refractive index of the glass core is set to be n1, the refractive index of the polymer core is set to be n2, and the refractive index of the polymer cladding is set to be n3, a ratio ZR = Z2core / Z1core of parameters Z2core and Z1core is within a range of 1.25 ≤ ZR ≤ 4, in which the parameter Z2core is defined as Z2core = a2 2 π/ 4 × √ (n1 2 -n3 2) and the parameter Z1core is defined as Z1core = a1 2 π/ 4 × √ n1 2 -n2 2) and the plastic glass optical fiber being characterised in that the parameter X is 1.8 or more. a glass core composed of glass; a polymer core composed of fluorine addition polymer, which is disposed around a periphery of the glass core, and has a refractive index lower than a refractive index of the glass core; and a polymer cladding composed of polymer, which is disposed around a periphery of the polymer core, and has a refractive index lower than the refractive index of the polymer core, wherein the plastic glass optical fiber satisfies following relations: a diameter a1 of the glass core is within a range between 110 μm or more and 200 μm or less, and when a diameter of the glass core is set to be a1 and a diameter of the polymer core is set to be a2, a parameter X defined as X = a2 2 /a1 2 is within a range of 1.15 ≤ X ≤ 2.9; and when a relative refractive index difference between the glass core and the polymer core is set to be Δ1 and a relative refractive index difference between the polymer core and the polymer cladding is set to be Δ2, a parameter Y defined as Y = Δ2/Δ1 is within a range of 0.25 ≤ Y ≤ 0.84X - 0.68 when the parameter X is within a range of 1.15 ≤ X ≤ 2, and the parameter Y is within a range of 0.48X - 0.71 ≤ Y ≤ - (2/9)X + 13/9 when the parameter X is within a range of 2 ≤ X ≤ 2.9; and when the diameter of the polymer core is set to be a2, the refractive index of the glass core is set to be n1, the refractive index of the polymer core is set to be n2, and the refractive index of the polymer cladding is set to be n3, a ratio ZR = Z2core / Z1core of parameters Z2core and Z1core is within a range of 1.25 ≤ ZR ≤ 4, in which the parameter Z2core is defined as Z2core = a2 2 π/ 4 × √ (n1 2 -n3 2) and the parameter Z1core is defined as Z1core = a1 2 π/ 4 × √ n1 2 -n2 2) and the plastic glass optical fiber being characterised in that the parameter X is 1.8 or more. a diameter a1 of the glass core is within a range between 110 μm or more and 200 μm or less, and when a diameter of the glass core is set to be a1 and a diameter of the polymer core is set to be a2, a parameter X defined as X = a2 2 /a1 2 is within a range of 1.15 ≤ X ≤ 2.9; and when a relative refractive index difference between the glass core and the polymer core is set to be Δ1 and a relative refractive index difference between the polymer core and the polymer cladding is set to be Δ2, a parameter Y defined as Y = Δ2/Δ1 is within a range of 0.25 ≤ Y ≤ 0.84X - 0.68 when the parameter X is within a range of 1.15 ≤ X ≤ 2, and the parameter Y is within a range of 0.48X - 0.71 ≤ Y ≤ - (2/9)X + 13/9 when the parameter X is within a range of 2 ≤ X ≤ 2.9; and when the diameter of the polymer core is set to be a2, the refractive index of the glass core is set to be n1, the refractive index of the polymer core is set to be n2, and the refractive index of the polymer cladding is set to be n3, a ratio ZR = Z2core / Z1core of parameters Z2core and Z1core is within a range of 1.25 ≤ ZR ≤ 4, in which the parameter Z2core is defined as Z2core = a2 2 π/ 4 × √ (n1 2 -n3 2) and the parameter Z1core is defined as Z1core = a1 2 π/ 4 × √ n1 2 -n2 2) and the plastic glass optical fiber being characterised in that the parameter X is 1.8 or more.