Abstract: A cylinder realizing reduced reciprocation friction between a piston ring and a bore surface of the cylinder in a region where the piston ring slides. The cylinder in which a piston slides on a bore surface of the cylinder. A plurality of recesses is formed in a stroke center region in the bore surface of the cylinder. The stroke center region is a region between an under face position of a ring groove for a bottom piston ring at a top dead center of the piston and a top face position of a ring groove for a top piston ring at a bottom dead center of the piston. The total of areas of all of the recesses is in the range of 1% to 80% when an area of the stroke center region is 100%, and the recesses are not formed in a region other than the stroke center region of the bore surface of the cylinder.