An automatic analyzer comprising: a reaction disk (6; 35) with reaction cells (12; 36) arrayed thereon; a dilution disk (3; 16, 17) with dilution cells (8; 18) annularly arrayed thereon; a mechanism (7, 9; 19, 20) for pipetting each parent sample (1; 38) from a sample array storage unit (2; 37) into each dilution cell (8; 18) and for delivering a liquid diluent to the dilution cell (8; 18) having the parent sample (1; 38) pipetted thereinto; a mixing mechanism (10; 21) for mixing the pipetted parent sample (1; 38) and the diluent in the dilution cell (8; 18); a diluted-sample sampling mechanism (11; 22) for pipetting into one of the reaction cells (12; 36) a diluted sample created by mixing the parent sample (1; 38) and the diluent in the dilution cell (8; 18); and control means , characterized in that two dilution disks are arranged to rotate concentrically about a common axis and are arranged such as to operate independently from each other, the control means is adapted to control a dilution process for the parent sample (1; 38) by assigning a fixed delay in the execution timing of the dilution process between the two dilution disks , and the control means has a control function that works such that while one of the dilution disks is being used for pipetting the diluted sample, the other dilution disk is used to execute parent-sample sampling, diluent delivery, and diluent/sample mixing, and such that after the pipetting of the diluted sample using the one dilution disk , the diluted sample is immediately pipetted from the other dilution disk , and the automatic analyzer is configured such that each of the respective mechanisms (7, 9-11; 19-22) can access both dilution disks . a reaction disk (6; 35) with reaction cells (12; 36) arrayed thereon; a dilution disk (3; 16, 17) with dilution cells (8; 18) annularly arrayed thereon; a mechanism (7, 9; 19, 20) for pipetting each parent sample (1; 38) from a sample array storage unit (2; 37) into each dilution cell (8; 18) and for delivering a liquid diluent to the dilution cell (8; 18) having the parent sample (1; 38) pipetted thereinto; a mixing mechanism (10; 21) for mixing the pipetted parent sample (1; 38) and the diluent in the dilution cell (8; 18); a diluted-sample sampling mechanism (11; 22) for pipetting into one of the reaction cells (12; 36) a diluted sample created by mixing the parent sample (1; 38) and the diluent in the dilution cell (8; 18); and control means , characterized in that two dilution disks are arranged to rotate concentrically about a common axis and are arranged such as to operate independently from each other, the control means is adapted to control a dilution process for the parent sample (1; 38) by assigning a fixed delay in the execution timing of the dilution process between the two dilution disks , and the control means has a control function that works such that while one of the dilution disks is being used for pipetting the diluted sample, the other dilution disk is used to execute parent-sample sampling, diluent delivery, and diluent/sample mixing, and such that after the pipetting of the diluted sample using the one dilution disk , the diluted sample is immediately pipetted from the other dilution disk , and the automatic analyzer is configured such that each of the respective mechanisms (7, 9-11; 19-22) can access both dilution disks . <EOS>