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 (16, 17) 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 (16, 17), and the control means has a control function that works such that while one of the dilution disks (16, 17) is being used for pipetting the diluted sample, the other dilution disk (17, 16) 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 (16, 17), the diluted sample is immediately pipetted from the other dilution disk (17, 16), and the automatic analyzer is configured such that each of the respective mechanisms (7, 9-11; 19-22) can access both dilution disks (16, 17). 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 (16, 17) 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 (16, 17), and the control means has a control function that works such that while one of the dilution disks (16, 17) is being used for pipetting the diluted sample, the other dilution disk (17, 16) 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 (16, 17), the diluted sample is immediately pipetted from the other dilution disk (17, 16), and the automatic analyzer is configured such that each of the respective mechanisms (7, 9-11; 19-22) can access both dilution disks (16, 17).