A cylinder block that can be used commonly in a longitudinally mounted engine and a transversely mounted engine without increasing a manufacturing cost. The cylinder block comprises an attachment flange joined to a transmission or a transaxle, and an oil pan or the oil pan and a ladder frame are attached to a lower end thereof. The attachment flange comprises: a first flange formed on an outer periphery thereof; a first joint surface formed on the first flange to be joined to a matching surface of the transmission; a second flange extending in the inner side of the first flange; and a second joint surface formed on the second flange to be joined to a matching surface of the transaxle.