The present invention provides an optical fiber in which composites constructing its coating are not complicated, so, there is also little constraint in view of production, and, moreover, delamination between a glass optical fiber and a primary layer, and a bubble in the primary layer hardly arise. The optical fiber of the present invention is an optical fiber which has a glass optical fiber which has a core 1, which passes an optical signal, in a center portion, and a cladding 2 surrounding this, a primary protective layer 3 made to coat the glass optical fiber, a secondary protective layer 4 applied on this primary protective layer 3, and a third protective layer 5 applied to an outer periphery of this secondary protective layer 4, wherein glass transition temperature of the primary protective layer 3 is made to be higher than −20° C. and 10° C. or lower, glass transition temperature of the secondary protective layer 4 is made to be −10° C. or less, and the glass transition temperature of the primary protective layer 3 is set higher than that of the secondary protective layer 4.