An optical fiber, comprising: a core (11, 21) provided at a central portion; an internal cladding coat (12, 22) provided around the core, having a refractive index less than a refractive index of the core (11, 21); a trench coating (13, 23) provided at a periphery of the internal cladding coat (12, 22) and constituted of two or more layers having different refractive indices; and an outermost cladding coat (14, 24) provided at a periphery of the trench coating (13, 23), wherein a layer having the highest refractive index in the trench coating (13, 23) configures an outermost layer of the trench coating, a layer having the lowest refractive index in the trench coating (13, 23) configures an innermost layer of the trench coating, the two or more layers constituting the trench coating (13, 23), wherein the layer that is provided adjacent inside the outermost layer has a refractive index lower than that of the outermost layer, characterized in that Δ core >Δ ic >Δ tmax >Δ tmin, -0.40%≥Δ tmin ≥-0.50%, -0.15%≥Δ tmax ≥-0.25%, and 0.45≤(r tmax -r in)/(r out -r in)≤0.9 are satisfied where a relative refractive index difference of the core (11, 21) is represented as Δ core, a relative refractive index difference of the internal cladding coat (12, 22) is represented as Δ ic, a relative refractive index difference of a layer having the highest refractive index in the trench coating is represented as Δ tmax, a relative refractive index difference of a layer having the lowest refractive index in the trench coating is represented as Δ tmin, a radius of an internal edge of the trench coating (13, 23) is represented as r in, a radius of an external edge of the trench coating (13, 23) is represented as r out, and a radius of an internal edge of a layer having the highest refractive index in the trench coating is represented as r tmax and where the relative refractive index differences are based on a refractive index of the outermost cladding coat (14, 24), in the trench coating (13, 23), the outermost layer has the lowest amount of dopant and the innermost layer has the greatest amount of dopant, and the trench coating (13, 23) is formed of silica glass into which only fluorine is introduced. a core (11, 21) provided at a central portion; an internal cladding coat (12, 22) provided around the core, having a refractive index less than a refractive index of the core (11, 21); a trench coating (13, 23) provided at a periphery of the internal cladding coat (12, 22) and constituted of two or more layers having different refractive indices; and an outermost cladding coat (14, 24) provided at a periphery of the trench coating (13, 23), wherein a layer having the highest refractive index in the trench coating (13, 23) configures an outermost layer of the trench coating, a layer having the lowest refractive index in the trench coating (13, 23) configures an innermost layer of the trench coating, the two or more layers constituting the trench coating (13, 23), wherein the layer that is provided adjacent inside the outermost layer has a refractive index lower than that of the outermost layer, characterized in that Δ core >Δ ic >Δ tmax >Δ tmin, -0.40%≥Δ tmin ≥-0.50%, -0.15%≥Δ tmax ≥-0.25%, and 0.45≤(r tmax -r in)/(r out -r in)≤0.9 are satisfied where a relative refractive index difference of the core (11, 21) is represented as Δ core, a relative refractive index difference of the internal cladding coat (12, 22) is represented as Δ ic, a relative refractive index difference of a layer having the highest refractive index in the trench coating is represented as Δ tmax, a relative refractive index difference of a layer having the lowest refractive index in the trench coating is represented as Δ tmin, a radius of an internal edge of the trench coating (13, 23) is represented as r in, a radius of an external edge of the trench coating (13, 23) is represented as r out, and a radius of an internal edge of a layer having the highest refractive index in the trench coating is represented as r tmax and where the relative refractive index differences are based on a refractive index of the outermost cladding coat (14, 24), in the trench coating (13, 23), the outermost layer has the lowest amount of dopant and the innermost layer has the greatest amount of dopant, and the trench coating (13, 23) is formed of silica glass into which only fluorine is introduced.