To provide a winding core ball lock device capable of simply and smoothly detaching a winding core from a spindle after completion of winding, and making it hard to damage an inner circumference of the winding core when the winding core is detached from the spindle.

In a winding core ball lock device for fixing a hollow winding core C covered on an outer circumference of a body member 2 of a spindle to the body member 2, an containing groove 9 extending along an inclined groove 5 and continued to the inclined groove 5 in a width direction is formed at a portion of the body member 2 on a spindle tip side of the inclined groove 5. A guide plate 10 made of an elastic material for partitioning the inclined groove 5 and the containing groove 9 is contained in the containing groove 9 so that the tip of the guide plate 10 is directed toward a deep portion of the inclined groove 5, and fixed to the body member 2 on a rear end side of the guide plate 10 so that the tip side of the guide plate 10 is flexed in a width direction of the containing groove 9. A window part 7 extends in the width direction of the body member 2 so that a sphere 6 can move toward a tip of the spindle on a bottom face 5c of the inclined groove 5.