PURPOSE: To achieve improved linearity and accuracy by extracting a sample completely through a sample loop and pushing out the exact amount.

CONSTITUTION: A small amount of flush solvent is extracted from the well of a flush solvent into an injector 4, and the injector 4 is switched to a transportation tube 16 leading to a sample tower 12. Then, when a small amount of air bubbles 8 are pulled out into a needle 10 that exists at the tower 12, a vial 14 is lifted into the tower 12. Then, a sufficient amount of sample 18 is extracted through a six-port valve 6 by the valve 6 located at 'injection' position, thus pushing out a desired amount of sample 18. Then, a small amount of samples 18 are pushed out to exclude backlash at the drive mechanism of the injector 4. Then, the six-port valve 6 is switched to 'filling' position, and a desired amount of sample 18 is pushed into a pool 20. Then, the six-port valve 6 is switched to 'injection' position, and a desired amount of sample is injected into an analysis column.