A machining status monitoring apparatus is provided on a machine tool, and has an actual CCD camera for imaging the tool and the workpiece and generating actual two-dimensional image data thereof, a virtual image generating section having a virtual CCD camera corresponding to the actual CCD camera, in which the tool and workpiece of three-dimensional model are imaged by the virtual CCD camera and virtual two-dimensional image data thereof are generated, and a display control section for receiving from a control device of the machine tool, information relating to the coolant supply state and checking whether coolant is being supplied to the contact portion of the tool and the workpiece, and displaying on a display device actual two-dimensional image data when coolant is not being supplied and displaying on the display device virtual two-dimensional image data when coolant is being supplied.