Adhering a belt edge tape to both respective side edge portions of the belt on the outer peripheral surface of the building drum by supplying a belt edge tape toward the outer peripheral surface of the building drum by pressing using an extruder which constitutes a supply device facing the building drum in an opposed manner and by pressing the tape to the building drum using a press roller on a leading side as viewed from a position where the tape is supplied in the rotational direction of the building drum, the building drum is rotated in the direction that end portions of the reinforcing cords on the side edge portion of the belt which constitutes a tape adhering side are positioned on a trailing side in the rotational direction of the building drum thus adhering the tape to the side edge portion.