A surgical instrument has a hollow tubular member, and a pressurization unit that has an outer valve portion, a pressurization device having a movable part configured to generate pressurized fluid when the movable part is moved, and an inner valve portion. The inner valve portion includes a first flow passage that is configured to fluidically connect a first port and a second port of the outer valve portion to each other when the inner valve portion is in a first position, and a second flow passage that is configured between the inner valve portion and the outer valve portion to fluidically connect the first port and a third port when the inner valve portion is in a second position. A sealing system fluidically isolates the second port and the third port from each other at any position of the inner valve portion. Pressurized fluid from the pressurization device causes the inner valve portion to move from the first position to the second position, thereby providing positive pressure to the hollow tubular member.