At an initial position in which a hub (40) is positioned at the front end of the lumen of a shield (20), an inner needle (50) passes through an outer needle (30) and protrudes from the tip of the outer needle. At a retracted position in which the hub is positioned at the back end of the shield lumen, the inner needle is withdrawn into the lumen of the shield. A first side pore (31) is formed in the outer circumferential surface of the outer needle and a second side pore (51) is formed in the outer circumferential surface of the inner needle. When the hub is at the initial position, the inner surface of the region of the outer needle (33) that comprises the first side pore is in close contact with the outer circumferential surface of the inner needle and the second side pore is positioned on the hub-ward side of the region where the inner surface of the outer needle and the outer circumferential surface of the inner needle are in close contact, thereby facilitating priming of the space between the inner needle and outer needle with blood and preventing leakage of blood from the side pore of the outer needle during puncture.Cuando un cubo (40) está en una posición inicial donde se encuentra en el lado del extremo frontal de una cavidad interior de una cubierta (20), una aguja interior (50) penetra una aguja exterior (30) y sobresale de un extremo delantero de la aguja exterior al exterior, y cuando el cubo está en una posición retraída donde se encuentra en el lado extremo posterior de la cavidad interior de la cubierta, la aguja interior está alojada dentro de la cavidad interior de la cubierta. Un primer orificio (31) lateral está formado en una cara circunferencial exterior de la aguja exterior, y un segundo orificio (51) lateral está formado en una cara circunferencial exterior de la aguja interior. Cuando el cubo está en la posición inicial, una cara circunferencial interior de una región (33) de la aguja exterior que contiene el primer orificio lateral está en c
