An automatic analyzer that has a function of performing optical measurement on a reaction solution which contains a sample and a reagent in a reaction container and cleaning of the reaction container, the automatic analyzer comprising: a disk mechanism on which a plurality of reaction containers having a shape of cylindrical or parallelepiped type are circumferentially disposed and a rotation operation of the reaction containers is controlled; a control apparatus adapted to control a sequence which includes the optical measurement and the cleaning; a block suction mechanism that includes a suction nozzle adapted to suction a liquid in the reaction container and a suction block attached to a lower end in a vertical direction of the suction nozzle and having the same type of cylindrical or parallelepiped shape as the reaction containers, and that is adapted to move the suction nozzle and the suction block up and down in the vertical direction and to suction the liquid; and a block cleaning mechanism adapted to clean the suction block, wherein the block suction mechanism and the block cleaning mechanism for a step of the cleaning of the reaction container are disposed on predetermined positions on a circumference of the disk mechanism, characterized in that the block suction mechanism is adapted to move the suction nozzle and the suction block into a stationary position in a reaction container, in which there are gaps of predetermined sizes between the side surfaces of the suction block and the reaction container and between the bottom surfaces of the suction block and the reaction container and to suction the liquid in the reaction container when the suction nozzle and the suction block are in the stationary position; and after receiving a start request of the optical measurement, the control apparatus is adapted to: cause, in the step of the cleaning of the reaction container that is provided before a step of the optical measurement and includes a plurality of cycles in which a unit movement of the disc mechanism is set as one cycle, both cleaning of the suction block by the block cleaning mechanism and suction of the liquid by the block suction mechanism to be performed in a first step that includes a plurality of cycles, and only the suction of the liquid by the block suction mechanism to be performed in a second step that includes one or more cycles, and cause the first optical measurement to be performed by using the reaction container in which the second step has been performed. a disk mechanism on which a plurality of reaction containers having a shape of cylindrical or parallelepiped type are circumferentially disposed and a rotation operation of the reaction containers is controlled; a control apparatus adapted to control a sequence which includes the optical measurement and the cleaning; a block suction mechanism that includes a suction nozzle adapted to suction a liquid in the reaction container and a suction block attached to a lower end in a vertical direction of the suction nozzle and having the same type of cylindrical or parallelepiped shape as the reaction containers, and that is adapted to move the suction nozzle and the suction block up and down in the vertical direction and to suction the liquid; and a block cleaning mechanism adapted to clean the suction block, wherein the block suction mechanism and the block cleaning mechanism for a step of the cleaning of the reaction container are disposed on predetermined positions on a circumference of the disk mechanism, characterized in that the block suction mechanism is adapted to move the suction nozzle and the suction block into a stationary position in a reaction container, in which there are gaps of predetermined sizes between the side surfaces of the suction block and the reaction container and between the bottom surfaces of the suction block and the reaction container and to suction the liquid in the reaction container when the suction nozzle and the suction block are in the stationary position; and after receiving a start request of the optical measurement, the control apparatus is adapted to: cause, in the step of the cleaning of the reaction container that is provided before a step of the optical measurement and includes a plurality of cycles in which a unit movement of the disc mechanism is set as one cycle, both cleaning of the suction block by the block cleaning mechanism and suction of the liquid by the block suction mechanism to be performed in a first step that includes a plurality of cycles, and only the suction of the liquid by the block suction mechanism to be performed in a second step that includes one or more cycles, and cause the first optical measurement to be performed by using the reaction container in which the second step has been performed. cause, in the step of the cleaning of the reaction container that is provided before a step of the optical measurement and includes a plurality of cycles in which a unit movement of the disc mechanism is set as one cycle, both cleaning of the suction block by the block cleaning mechanism and suction of the liquid by the block suction mechanism to be performed in a first step that includes a plurality of cycles, and only the suction of the liquid by the block suction mechanism to be performed in a second step that includes one or more cycles, and cause the first optical measurement to be performed by using the reaction container in which the second step has been performed.