To provide a cylinder block constructed to be separated into a cylinder liner portion and a cylinder block body for more easily securing the supporting rigidity of the cylinder liner portion.

The cylinder block 3 is constructed to be separated into the cylinder liner portion 21 as part of the wall face of a cylinder and the cylinder block body 30 having a cylinder outer wall 32 encircling the cylinder liner portion 21. An approximately flat upper deck portion 22 provided on the top of the cylinder liner portion 21 is supported on a top 32a of the cylinder outer wall 32. A shim 70 is held between a bottom face 28 of the cylinder liner portion 21 and the cylinder block body 30 (a bottom face 41) opposed to the bottom face 28. Thus, the cylinder liner portion 21 is further supported at its lower part on the cylinder block body 30 via the shim 70.