Provided is a vascular anastomosis device for favorably anastomosing two blood vessels with different diameters. T he vascular anastomosis device comprises two rings with pins 21 made of a flexible material and an openable ring holder 2 2, which is made of a pair of components and detachably hold s the rings with pins 21, the ring holder 22 has a means for deforming the rings with pins, the end portion of the large-diameter blood vessel is inserted through a ring 21 and the vascular wall is extended outward 90 degrees and impaled on the pins, the end portion of the small-diameter blood vessel is inserted through the other ring 21, an incision is made i n a longitudinal direction from the end surface of the small -diameter blood vessel, the two rings 21 are elliptically de formed into a same elliptical shape by the means for deformi ng the rings so that the minor axis agrees with the diameter of the small-diameter blood vessel, the small-diameter blood vessel is elliptically opened and the vascular wall is exte nded outward 90 degrees and impaled on the pins, and the two rings 21 are joined together by allowing the pins provided o n the ring in one component to stick into the ring in the oth er component.
