A puncture needle cartridge comprising: a lancet having an elongate lancet body having a puncture needle at one end and a portion to be held by a puncture device at the other end, and a puncture needle cap for protecting the puncture needle; and a cylindrical puncture needle holder for holding the lancet body so that the lancet body is movable in the holder, characterized in that four linear grooves for guiding the movement of the lancet body are formed within the cylindrical puncture needle holder and extending in its axial direction from a first end partway to a second end of the puncture needle holder, the lancet body has: an elastically deformable arm means for restricting the movement of the lancet body in relation to the cylindrical puncture needle holder in a position where the puncture needle does not protrude from the puncture needle holder; a first convex portion for engaging with the grooves; and a second convex portion located in a positon outside the second end of the cylindrical puncture needle holder when the lancet body is stored in an inner-diameter part of the cylindrical puncture needle holder, the grooves reach an end surface of the first end, so that the lancet body can be inserted from the first end into the cylindrical puncture needle holder, the second convex portion has a difference in level on the side having the puncture needle and has a shape in which the height from the central axis of the lancet body decreases toward the end of the side not having the puncture needle, as well as comprises an elastically deformable material, and the rear end of the arm means and the first convex portion can contact a contact part provided on a rear end portion of the cylindrical puncture needle holder in order for the lancet body not to come out of the second end of the cylindrical puncture needle holder. a lancet having an elongate lancet body having a puncture needle at one end and a portion to be held by a puncture device at the other end, and a puncture needle cap for protecting the puncture needle; and a cylindrical puncture needle holder for holding the lancet body so that the lancet body is movable in the holder, characterized in that four linear grooves for guiding the movement of the lancet body are formed within the cylindrical puncture needle holder and extending in its axial direction from a first end partway to a second end of the puncture needle holder, the lancet body has: an elastically deformable arm means for restricting the movement of the lancet body in relation to the cylindrical puncture needle holder in a position where the puncture needle does not protrude from the puncture needle holder; a first convex portion for engaging with the grooves; and a second convex portion located in a positon outside the second end of the cylindrical puncture needle holder when the lancet body is stored in an inner-diameter part of the cylindrical puncture needle holder, the grooves reach an end surface of the first end, so that the lancet body can be inserted from the first end into the cylindrical puncture needle holder, the second convex portion has a difference in level on the side having the puncture needle and has a shape in which the height from the central axis of the lancet body decreases toward the end of the side not having the puncture needle, as well as comprises an elastically deformable material, and the rear end of the arm means and the first convex portion can contact a contact part provided on a rear end portion of the cylindrical puncture needle holder in order for the lancet body not to come out of the second end of the cylindrical puncture needle holder.