PURPOSE: To dispense with a precision mechanism and a checking process for positioning on the occasion of fitting by making a rack supply element, an analysis unit element and a rack accommodation element separable from each other and by fitting a rack conveying element integrally to the analysis unit element.

CONSTITUTION: Rack conveying elements 10 and 12 are fitted integrally to analysis unit elements 4 and 6 respectively. Positioning pins 26 and 28 for positioning each element when a rack supply element 2, the analysis unit elements 4 and 6 and a rack accommodation element 8 are assembled are provided on the lateral sides of each element. Positioning is made in such a manner that the positioning pin 26 of the supply element 2 is combined with the positioning pin 28 of the unit element and the positioning pins 26 and 28 in a pair are combined likewise for each pair of corresponding elements. Since the rack conveying element and the analysis unit element are integrated with each other, the positional relationship between a rack stop position and a suction stop position of a pipette for which the highest positioning precision is requested is always maintained correctly irrespective of separation and fitting of each element, fine positioning adjustment is dispensed with, and thus an apparatus can be constructed inexpensively.