To provide a cap which can facilitate the cap opening and closing of a plastic bottle or the like by one hand, and has an opening and closing mechanism of a conventional rotary system.

By forming a structure wherein a plurality of vertical incisions (slits) are formed at the periphery of a cap lateral part of a conventional plastic bottle or the like, cap opening operation can be performed by one hand in a one-touch manner using an external force. In addition, the cap opening operation of the rotary system can be also performed in the case of the container opening and closing operation of the conventional plastic bottle or the like.