To simplify the structure by dispensing a special mechanism in an oscillatory stop device.

When a loading unit is positioned right above the center O of a main shaft, a loader hand 6 is tilted to lower a loader arm 5 to a position such that the vertical distance R1 between the center O of the spindle and the center O of turn of the loader hand 6 is equal to the radius R of turn of the axis 2 of a work W. Subsequently, the loader hand 6 is turned toward the center O of the main shaft and stopped on the same vertical line as the loader arm 5. Whereupon, by setting R1=R, the center O of the main shaft is positioned on the locus of turn of the axis of the work W, so that the work W enters between the rocking arms 14, 14 to automatically position the axis O in the center O of the main shaft.