It is an object of the present invention to provide an infusion device that can be easily inserted into the body and that when inserted into a blood vessel reliably ensures the flow of blood. The infusion device is provided with a needle-shaped tube member(12) having a sharp tip in any one lumen of the three lumens provided within a tubular member that can be inserted into the body in such a manner that it can move axially, an extrusion aperture(22) provided in the tubular member through which the needle-shaped tube member is extruded,and a reagent supplier for supplying a predetermined reagent into the needle-shaped tube member. Additionally, recessed portions extending axially are formed in an outer circumferential surface of the tubular member in such a manner that the cross sectional shape perpendicular to the axial direction of the tubular member is a shape in which at least a portion of the outer circumference of an annular shape has been recessed radially inward.