Disclosed is an exhaust purification device for an internal combustion engine provided with a venturi-shaped mixing chamber (13) upstream of a NOx catalyst (16), said mixing chamber (13) formed continuously from a tapering part (13a) along which the radius decreases in the downstream direction, a waist part (13b) at which the radius is at smallest, and a widening part (13c) along which the radius increases in the downstream direction. A vane plate (18) and an aqueous urea solution spray nozzle (19) are arranged inside the tapering part (13a). The ratio (a/b) of the distance (a) between the vane plate (18) and the center of the waist part (13b) and the distance (b) between the center of the waist part (13b) and the mouth of the NOx catalyst (16) is set between 0.5 and 1.0.