A vascular anastomosis apparatus using a carbon dioxide laser is proposed. The vascular anastomosis apparatus satisfies three conditions: a long focal distance of not less than 10 cm which is suitable for surgical operations under microscopic observation; a beam spot diameter of 0.1 to 0.3 mm when a laser beam is converged; and a stable, small beam output of not more than 100 mW. A visible guide beam having the same focusing point as that of the carbon dioxide laser beam is used in the vascular anastomosis apparatus.