A sample injection device (100) includes a tubular suction and discharge unit (23) configured to suction a liquid sample (S), contain the sample therein, and discharge the suctioned sample, and at least a portion of an inner wall (23a) of the suction and discharge unit, the portion having the sample contained therewithin, is subjected to a surface treatment (V) to increase an interfacial tension (F) that acts between the inner wall and the sample.