To provide a can cap which can be engaged with cans having different outer diameters by a small press force.

The can cap includes an upper face portion and a side wall portion extended down on the outer periphery of the upper face portion and composed of a plurality of thin-walled portions and thick-walled portions arranged alternately in the circumferential direction, the side wall portion having a first side wall extended down at least on the outer periphery of the upper face portion and a second side wall connected to the first side wall and larger in bore diameter than the first side wall. The can cap also includes a plurality of second locking portions formed to project from the vicinity of the lower end of the thick-walled portions of the second side wall toward the inside of the cap, a plurality of first locking portions formed to project from the vicinity of the lower end of the thick-walled portions of the first side wall toward the inside of the cap, and a stopper formed to project toward the inside of the cap above the first locking portions of the thick-walled portions of the first side wall. The second locking portions or the first locking portions are engaged with a screw-tightening portion of the can. In this manner, the can cap is attached to cans having different outer diameters.