To provide a technique relating to a method for manufacturing a cylinder block, which technique facilitates removal of a core material by a simple structure regardless of a casting method to be used.

In the method for manufacturing a cylinder block 5, the process of casting the cylinder block 5 includes: a step of transferring a thermal injection layer 3 on the inner surface of the cylinder block 5 by casting-in a core 4, which consists of a releasing material layer 2 formed on the outer peripheral surface of a core material 1 and the thermal injection layer 3 formed on the outer peripheral surface of the releasing material layer 2 (that is, a thermal injection layer transferring step); a step of removing the core material 1 from the cylinder block 5 (that is, a core material removing step); and a step of removing the releasing material layer 2 remaining on the inner surface of the cylinder block 5 (that is, a releasing material layer removing step). The releasing material layer 2 is formed of an easily breakable refractory.