To provide a cap structure which enables a quantity of contents to be poured out to be arbitrarily controlled and the contents to be poured out without bending a hand to an unnatural shape.

The cap structure comprises a cap body 100 and an open/close upper cap 200. The cap body has an attaching tube 130 standing on its top 110, with a pour- out hole 131 bored on one of sides of the attaching tube. The outer peripheral surface opposite to the pour-out hole is equipped with a slide-contact groove 132 having a width symmetric toward right and left peripheral directions from the opposite position. An engaging groove 133 is provided on the outer peripheral surface on a lower part other than the slide-contact groove. An engaging ring with a container is provided on the inner peripheral surface at the lower end of a peripheral wall 120. The open/ close upper cap comprises an inner peripheral wall 220 having a top 210 connected with the upper end, an outer peripheral wall 230, a base plate 240 and a pour-out tube 250. A pour-out hole 201 connected with the inner peripheral wall, the pour-out tube and the outer peripheral wall is bored. A locking rib 221 extending from the upper end to the lower end is provided on the outer peripheral surface of the inner peripheral wall facing the pour-out hole, and an engaging ring 222 with the cap body is provided on the inner peripheral surface at the lower end of the inner peripheral wall.