PURPOSE: To obtain a sample feeder in which a sample can be sucked depending on the container thereof by a constitution wherein a needle automatically detects the position of sample container located at any position.

CONSTITUTION: The sample feeder comprises an externally threaded rod 5 fixed between a balance 1 and a bottom plate 2 rotatably through a driver, and a needle holder 10 mounting a needle 11 with an internal thread 12 meshing the externally threaded rod 5 being arranged while being supported by a spring 9. When an external thread 5 is driven by means of a stepping motor 7 and the needle 11 abuts, at the forward end thereof, against the bottom of a sample container 21, the needle holder 10 is stopped thereat and the internal thread 12 supported by the spring 9 lowers slightly furthermore. A shielding plate 15 and a photointerrupter 16 detect the slight lowering of internal thread 12 and the moving distance of needle 11 from the origin (number of revolutions of the externally threaded rod) is determined based on the number of pulses of stepping motor 7.