To prevent the occurrences of poor demolding caused by sticking of a binder fiber which gives a shape retention capacity and a snag prevention property of a fiber bundle to a mold of a fiber-reinforced composite material when a preform is constituted by a three-dimensional fiber structure.

The preform is constituted by a three-dimensional braiding 11 composed by braided threads 12 and core threads 13. The braided thread 12 is formed of a thread strip 16 in which a binder fiber 15 is wound in spirals outside the fiber bundle 14 of continuous fibers. The binder fiber 15 is positioned inside the three-dimensional braiding 11 and is fused to the fiber bundle 14. The winding pitch of the binder fiber 15 to the fiber bundle 14 is set so as to be larger than the length of part 12a in which the braided threads 12 are exposed on the surface of the three-dimensional braiding 11, and at the same time, so as to be in a winding state that the binder fiber 15 is positioned only inside the three-dimensional braiding 11.