PURPOSE: To detect a container different in diameter in an apparatus for scanning and centering the container on a tray.

CONSTITUTION: An analyser has a scanning apparatus 1 for the body fluid filled container different in diameter on a tray 5 and the scanning apparatus 1 is arranged at a sucking position. A scanning means has two movable scanning members 2, 3 and the sensors 16 are connected to the scanning members 2, 3 to be driven thereby. The scanning members 2, 3 cross a revolving feeder 40 forming a container feed passage at a right angle to be held to the initial position to the feed passage by two springs. When the feeder is revolved to the scanning position from a tray rack, the scanning members are moved to an end part position and a sensor generates the signal corresponding to the diameter of the container present at the scanning position. The container is centered within the tray by the scanning members and the springs to be fixed.