A workpiece positioning device (1) includes a first positioning block (Bx) positioning one surface of a workpiece at a first reference surface in a first direction, two second positioning blocks (By1, By2) positioning a different surface of the workpiece at a second reference surface in a second direction, seat blocks (Bz1, Bz2, Bz3) positioning the workpiece in a third direction perpendicular to the first direction and the second direction, a push cylinder (30) pressing the workpiece in one direction toward an intersection line between the first and the second reference surface, a first unit (10) contacting with the one surface of the workpiece and correcting a posture of the workpiece before the first positioning block contacts with the workpiece, and a second unit (20) contacting with the different surface of the workpiece and correcting the posture of the workpiece before the second positioning blocks contact with the workpiece.