Medical tube

A medical tube comprising:

• an elongated main shaft tube that has a distal end and a proximal end, that has a distal opening on a distal side, and that internally has a lumen which communicates with the distal opening;
• a lateral introduction portion that is disposed at an intermediate position in an axial direction of the main shaft tube, and that introduces a fluid to the lumen from a boundary portion which connects a plurality of biological organs to each other;
• and
• a flow path opening/closing mechanism that is operable to be in a state of opening the lumen and to be in a state of closing the lumen, wherein the flow path opening/closing mechanism closes the lumen, when negative pressure is applied to the lumen on a proximal side further from flow path opening/closing mechanism, and opens the lumen, when positive pressure is applied to the lumen on a distal side further from the flow path opening/closing mechanism or when the negative pressure is released, and wherein the fluid is aspirated into the lumen via the lateral introduction portion by the negative pressure, and flows inside the main shaft tube in a proximal end direction.