In an object positioning/fixing device that positions and fixes a target object on a base member in the horizontal direction and in the vertical direction, a structure is provided in which, in a state in which the target object is pressed against the base member and fixed thereon by a fixation mechanism: first and second tapered engagement surfaces of first and second reference members are closely contacted against the inner circumferential surfaces of first and second annular engagement members via elastic deformation of the first and second annular engagement members; also first and second base end contact surfaces of the first and second reference members are contacted against the base member; and a pair of regulated surfaces of the second annular engagement member are closely contacted against a pair of regulating surfaces of a second installation hole via elastic deformation of the second annular engagement member.