An anastomosis instrument adapted to be used with an endoscope, the anastomosis instrument comprising: a puncture needle adapted to be moved reciprocally inside a first channel that is provided in an insertion portion of the endoscope that the insertion portion has the first channel and a second channel, the insertion portion is adapted to be inserted into a body cavity, and the puncture needle is adapted to protrude from a distal end of the insertion portion so as to puncture a living body tissue; and a space retaining device that is positioned in front of a distal end of the puncture needle, and that provides a predetermined clearance between the living body tissue that is to be punctured that is loaded in the distal end of the insertion portion, and the living body tissue that is not to be punctured that is positioned further from the puncture needle than the living body tissue that is to be punctured; characterized in that the anastomosis instrument further comprises: a distal end cap having a ring shaped fitting portion adapted to be fitted onto a distal end of the insertion portion; and a connecting portion which fixes the space retaining device and the distal end of the fitting portion; wherein an inner diameter of the fitting portion is substantially equal to an outer diameter of the distal end of the insertion portion, and the space retaining device is located at a position away from the center of the fitting portion when viewed from an insertion direction in which the insertion portion is inserted into the fitting portion so that the space retaining device is not provided in the direction in which a grasping forceps protrudes from the second channel. a puncture needle adapted to be moved reciprocally inside a first channel that is provided in an insertion portion of the endoscope that the insertion portion has the first channel and a second channel, the insertion portion is adapted to be inserted into a body cavity, and the puncture needle is adapted to protrude from a distal end of the insertion portion so as to puncture a living body tissue; and a space retaining device that is positioned in front of a distal end of the puncture needle, and that provides a predetermined clearance between the living body tissue that is to be punctured that is loaded in the distal end of the insertion portion, and the living body tissue that is not to be punctured that is positioned further from the puncture needle than the living body tissue that is to be punctured; characterized in that the anastomosis instrument further comprises: a distal end cap having a ring shaped fitting portion adapted to be fitted onto a distal end of the insertion portion; and a connecting portion which fixes the space retaining device and the distal end of the fitting portion; wherein an inner diameter of the fitting portion is substantially equal to an outer diameter of the distal end of the insertion portion, and the space retaining device is located at a position away from the center of the fitting portion when viewed from an insertion direction in which the insertion portion is inserted into the fitting portion so that the space retaining device is not provided in the direction in which a grasping forceps protrudes from the second channel. a distal end cap having a ring shaped fitting portion adapted to be fitted onto a distal end of the insertion portion; and a connecting portion which fixes the space retaining device and the distal end of the fitting portion; wherein an inner diameter of the fitting portion is substantially equal to an outer diameter of the distal end of the insertion portion, and the space retaining device is located at a position away from the center of the fitting portion when viewed from an insertion direction in which the insertion portion is inserted into the fitting portion so that the space retaining device is not provided in the direction in which a grasping forceps protrudes from the second channel.