Medical instrument introduction device and treatment method of using the same

A medical instrument introduction device, comprising:

• an outer tube portion that is configured to be indwelled within a body wall;
• and
• an inner needle portion that is configured to be inserted through the outer tube portion,
• wherein the outer tube portion includes:
• a base portion disposed at a proximal side of the outer tube portion;
• a tubular conduit portion, the conduit portion being formed of a stretchable material, a proximal end portion of the conduit portion being connected to the base portion;
• and
• an anchor portion connected to a distal end portion of the conduit portion,
• wherein:
• the conduit portion has a bellows folded shape in a natural state,
• a dimension of the conduit portion in an axial direction is capable of being increased as the folded shape is stretched by the inserted inner needle portion, and a force needed for stretching and increasing the dimension of the folded shape in the axial direction is gradually decreased in a direction from the proximal end portion toward the distal end portion of the conduit portion, such that the distal end portion of the folded shape stretches first when the inner needle portion is inserted into the conduit portion and exerts force on the folded shape, and
• the anchor portion and the inner needle portion are couplable with each other such that the anchor portion moves following an advancement or a retraction of the inner needle portion.