An optical fiber comprises a glass fiber which comprises a core and a cladding, a primary resin coating layer which covers the periphery of the glass fiber, and a secondary resin coating layer which covers the periphery of the primary resin coating layer. The glass fiber is a multimode fiber having a core diameter of 40-60 μm and a cladding diameter of 90-110 μm, and the primary resin coating layer is a layer formed by curing a curable resin composition which comprises oligomers, monomers, and a reaction initiator, the curable resin composition containing a one-end-capped oligomer in an amount of 30% by mass or larger based on all the oligomers.