In order to introduce a sample X into a particle size distribution measuring apparatus 200 while neither using a large amount of liquid nor leaving the sample X, a sample introduction system that introduces the sample X into the particle size distribution measuring apparatus 200 that measures the particle size distribution of the sample X is adapted to include: a sample load part 20 that has a load space S into which the sample X is loaded, and a lead-out port 20a adapted to lead out the sample X loaded into the load space S; and a liquid supply mechanism 50 adapted to, into the load space S, supply liquid that is mixed with the sample X and provided in order to measure the particle size distribution. In addition, the sample introduction system is also adapted such that the liquid supplied by the liquid supply mechanism 50 is conducted to the lead-out port 20a while circulating along an inner circumferential surface 24 forming the load space S of the sample load part 20.