PURPOSE: To enable an annular core to be inserted into a core frame without exerting large external force, by holding the winding core secured to the annular core by means of a winding chuck mechanism while attracting the axial end face of the annular core by means of electromagnets.

CONSTITUTION: When an annular core 6A is positioned at a position to be attracted, a movable member 23 is conveyed to the core attracting position. The central axis of the annular core 6A then coincides with the axis passing the center of the circle along which electromagnets 34A to 34C are arranged. When it is detected that the electromagnets have reached the core attracting position, a cylinder 30 is driven so that a vertically movable plate 32 is lowered. The descent of the plate 32 first causes a chucking claw 42 of a winding core chucking mechanism to enter into a winding core 61 of the annular core 6A at the core attracting position, whereby the stopper portion 42a of the chucking claw 42 is applied against the upper end face of the winding core 61. When it is detected that the stopper portion has been applied thereagainst, a cylinder 38 is driven so that a chuck driving plate 41 is driven toward the winding core 61, and the claw portion 42a of the chucking claw 42 is engaged in a claw engaging groove 61a provided on the inner periphery of the winding core. Thus, the winding core 61 is held securely by the chuck mechanism.