To facilitate forming a breather hole for relieving a pressure change of a crank chamber, in a cylinder block in which a storage space of a timing chain is integrally formed inside.

The cylinder block 10 includes the storage space 31 of the timing chain 41, the space being integrally formed inside. In the cylinder block: the breather hole 21 for relieving the pressure change of the crank chamber 20 is disposed on a bulkhead 17 supporting a journal 16a of a crankshaft 16; a through-hole 35 is disposed, coaxially with the breather hole 21, on an outer wall 30 forming the storage space 31 of the timing chain 41; a case member 80 covering the through-hole 35 is disposed on an outside surface of the outer wall 30; and a plate member 83 is disposed on a position where a blow-by gas flowing out via the breather hole 21 and the through-hole 35 collides, in the case member 80.