To provide an autoanalyzer unnecessary for delaying the moving speed of a cuvette even if the cuvette is miniaturized and capable of keeping the number of the cases in analytical processing.

The autoanalyzer 1 is constituted so as to measure the optical characteristics of a liquid when the cuvettes C moved while holding the liquid traverse luminous flux and has a light source 14a for irradiating the cuvettes with parallel light of which the luminous flux diameter along the moving direction of the cuvettes is larger than the width of each of the cuvettes, a plurality of the cuvette housing parts 4a provided along the moving direction of the cuvettes so as to keep the relative position with the cuvettes, a cuvette wheel 4 having guide holes smaller than the width of each of the cuvettes in its dimension along the moving direction of the cuvettes and opened to the respective housing parts to guide the passage of luminous flux and the light sensor 14d arranged at a position relatively constant with respect to the light source and characterized in that the dimension of the light detecting region along the moving direction of the cuvettes is larger than the width of each of the cuvettes and the signal corresponding to the quantity of the light passed through the cuvettes and the guide holes is outputted from the light detecting region.