A puncture device is provided that does not allow an outer needle to collapse or rise at the time of puncture and exhibits small puncture resistance.A puncture device 1 includes: a hollow outer needle 2; an outer needle hub 3 provided at a proximal end portion of the outer needle 2; a hollow inner needle 4 inserted into the outer needle 2 for use; and an inner needle hub 5 provided at a proximal end portion of the inner needle 4. The inner needle 4 includes, from the distal side, a sharp needlepoint 41, a small diameter portion 42 having an almost uniform outer diameter; an intermediate portion 43 formed as a tapered portion which is progressively increased in outer diameter as it goes toward the proximal end; and a larger diameter portion 44 having inner and outer diameters larger than inner and outer diameters, respectively, of the small diameter portion 42. If the puncture device 1 is assembled, the needlepoint 41 is most projected from the distal opening 24 of the outer needle 2 and the proximal end of the small diameter portion 42 and the distal end of the large diameter portion 4 are located inside the outer needle 2. The inner diameter of the outer needle 2 at a portion L1 where the outer needle 2 covers the small diameter portion 42 of the inner needle 4 is smaller than the large diameter portion 44 of the inner needle 4.