PURPOSE: To lengthen the service life of a cutting tool of a machine tool used at the time of machining a cylinder head joint surface of a cylinder block, to carry out cutting work efficiently and to reduce time required for a joint surface machining process.

CONSTITUTION: It is cylinder block structure in which a sleeve 6 is buried inside of a cylinder block main body 5 and the inside of the sleeve 6 is made to be a space 7 for arrangement of a piston. Additionally, the sleeve 6 is constituted so that one end surface of a cylinder block on the side of a cylinder head joint surface is arranged as it is positioned inward in the cylinder block main body 5 rather than the cylinder head joint surface 8 and the space 7 for piston arrangement is open to the cylinder head joint surface 8 through an inside part 10 of the cylinder block main body 5 covering the one end surface of the sleeve 6 from the inside of the sleeve 6.