An automatic sample analyzer includes: a pipette, a pipette driving device which moves the pipette to a sample vessel present in a predetermined position to cause the pipette to suck up a sample from the sample vessel, and then moves the pipette to an open vessel provided in another predetermined position to cause the pipette to discharge the sample into the open vessel, and an analyzing section for analyzing the discharged sample, the pipette driving device comprising a vertically movable main arm and an elongated guide arm cantilevered by the main arm and extending horizontally, the guide arm having a smaller flexural rigidity than the main arm, wherein the main arm vertically moves the pipette when the sample is to be sucked up from the sample vessel, and the guide arm guides the pipette to the open vessel and then vertically moves the pipette when the sample is to be discharged into the open vessel.