To provide a cylinder block having positioning accuracy between a bearing portion and a cylinder block body, good workability and production efficiency and lighter weight and higher strength.

A crank cap pair 2, in which cap side insertion holes 9 are made, is divided into crank caps 1 by cracking. The crank caps 1 are placed on a cap placement portion 13 of a male mold 11 for clamping and aluminum melt is poured into a cavity 17 to cast the cylinder block body 3. Then, the cylinder block body 3 to which the crank caps 1 are joined is removed therefrom and fixed thereto with a chucking tool 21, tapping work is applied to a cap side insertion hole 9 and a body side insertion hole 20, and the crank caps 1 are parted from the cylinder block body 3 by cracking. A crank shaft 5 is held therebetween and the crank caps 1 are fixed to the cylinder block body 3 with a bolt 7 to obtain the cylinder block 26.