A puncture needle (10) protrudes from the center of an approximately cross-shaped top plate (20) from which four arms (21) are protruded. From the tip of each of the arms, two elastic pieces (22) divided by a slit (23) extend toward the same side as the puncture needle. The tips of the two elastic pieces extending respectively from two adjacent arms are joined via a bridging portion (24) so as to form an approximately U-shaped holding piece (25). An engaging claw (30) protrudes toward the puncture needle from the bridging portion of the holding piece. The engaging claw can be displaced in a direction away from the puncture needle by elastic deformation of the elastic pieces.
