An article positioning mechanism for positioning an article comprising a component or a tool with respect to a mounting portion of a movable member of a mechanical device and also restraining rotation thereof includes a holder member to which the article is fixed and a frame shaped member that is fixed to the mounting portion, the holder member including position regulation surfaces and a tapered male engagement portion that is formed as a regular polygon and also is sloped so as to approach its axis in the direction towards the mounting portion, the frame shaped member including a reference surface that receives the position regulation surfaces and positions them in the axial direction, and a tapered female engagement portion that is formed as a regular polygon and also is sloped in the same direction as the tapered male engagement portion.