To provide a simply openable container having a simple opening formed by breaking thinned lines on a lid part, in which the tip of a straw can be easily aligned with the center of the simple opening and the thinned lines can be surely broken by the straw.

A recess 17 having one point on the lid part (top face part 11 of a cap 1) as the lowest point to be inwardly recessed from the external surface side of the lid part (top face part 11) and consisting of a tilted surface 17a tilted upward and outward from the lowest point is formed as the simple opening 16. In addition, at least three or more thinned lines 18 having the lowest point of the recess 17 as the intersection and radially extending to the vicinity of the outer periphery of the recess 17 are formed.