An optical fiber core consists of an optical fiber, an ultraviolet curable resinous layer which covers an outside circumferential part of an optical fiber, and a covering layer covering an outside circumferential part of ultraviolet curable resinous layer. In addition, the covering layer is composing of a first covering layer using flexible thermoplastic resin and second covering layer using thermoplastic resin of semi-hard or hard material in order that it sufficiently fulfills squeezing, tensile, bending, temperature, and lateral pressure characteristics and an economic efficiency.