Disclosed herein is a bottle cap with an additive supplying structure. The bottle cap includes an additive holding unit which is supported in a mouth of a bottle by an upper flange, has in a side surface of a lower portion thereof an opening for discharging the additive, and is open at the top. An open-and-shut unit is seated to be coaxial with the additive holding unit and moves up and down to open or shut the opening. An outer cap unit includes a sealing tube which is placed between the open-and-shut unit and the additive holding unit and performs a sealing function, an outer cap body which supports at a center thereof the sealing tube and is fastened to the mouth of the bottle through a screw-type fastening method, and a coupling part which is provided on the inner wall of the upper end of the sealing tube to be coupled to the open-and-shut unit. A skirt having a forgery preventing function is integrally provided on a lower end of the outer cap body and is secured to a skirt locking ring of the bottle, and a delay hook is provided on an inner wall of the skirt and retains the skirt for a period when the opening is opened by turning the outer cap unit, thus delaying separation of the skirt.