The present invention provides a needle tip protector of a novel structure for an indwelling needle, which enables improvements in safety, etc. as compared with conventional needle tip protectors. A needle tip protector 10 for an indwelling needle includes a tubular peripheral wall 58, and is externally attached over a needle hub 22 of an indwelling needle 16 and moved toward a needle tip 14 side so as to cover the needle tip 14. Detents 74, 74, which are to be detained with the needle hub 22 at a position in a movement of the protector toward the needle tip 14 side of the indwelling needle 16 so as to inhibit backward movement of the protector to the proximal end side of the indwelling needle 16 and to prevent the needle tip 14 from being reexposed, are formed within an inside enclosed by the peripheral wall 58, and are integrally molded with the peripheral wall 58.