A medical apparatus for joining body lumens in a living body includes a puncture member having a lumen, a distal opening portion and a needle tip at the distal end of the lumen. The needle tip can puncture a tube wall of the body lumen to form a puncture site. The medical apparatus includes a tubular member in the lumen of the puncture member that expands radially outward and contracts radially inward and a plunger movable relative to the puncture member to release the tubular member from the distal opening portion of the puncture member. The tubular member expands to be fixed to the puncture site when the tubular member is released from the distal opening portion of the puncture member.