PROBLEM TO BE SOLVED: To provide a blood sampling instrument which permits an instrument user himself to easily recover a thing dropped even if he unexpectedly drops the thing into the clearance between a housing and a tray.SOLUTION: The blood sampling instrument 1 includes the tray 40 on which a blood bag is mounted, a rocking mechanism 50 rocking the tray 40, a first positioning portion 60 arranged on the side facing the rocking mechanism 50 in the tray 40 and a second positioning portion 70 arranged on the side facing the tray 40 in the rocking mechanism 50. The tray 40 and the rocking mechanism 50 are detachably formed through the first positioning portion 60 and the second positioning portion 70. The first positioning portion 60 and the second positioning portion 70 are formed of prescribed concave and convex patterns engaging with each other by concavity-convexity fitting and formed to permit the tray 40 to be positioned with respect to the rocking mechanism 50 by the concave and convex patterns.
