An operation limiting device applicable to a wide variety of machine tools and which improves the freedom of setting an operation limiting area. Two or three drive axes (Xa, Za) in different directions are designated from among a plurality of drive axes in the machine tool and the designated drive axes (Xa, Za) form the two or three dimensional coordinate system. An area (Ar) for limiting the operation of the mobile body is set in the two or three dimensional coordinate system. A drive axis (Xa) which is in operation is determined, and in the two or three coordinate system including the drive axis which is in operation the operation of the mobile body is limited when the mobile body enters into the limiting area (Ar).