To provide a hinge cap for reliably preventing ingress of dust and water if a lid body is closed, and stably maintaining an open condition of the lid body if the lid body is opened even when a vessel is toppled.

In the cap having a base which is fitted to a mouth of a vessel and has an open hole to discharge contents in the vessel, and a lid body which is fitted to the base to close the open hole, at least two leaf springs erected parallel to each other and separated from a side wall are provided on an upper end of the side wall of the base, and an edge of the lid body is connected via a hinge in an oscillating manner at each tip of the leaf springs. A slidable tongue piece which is located between the leaf springs and slides on the side wall of the leaf spring to elastically deform the leaf springs is provided on the lid body.