To provide a machining jig of a cylinder block configured to reproduce a deformed shape of a cylinder bore by uniformly applying contact pressure to a peripheral part of the cylinder bore with simple configuration, and to provide a method of manufacturing the cylinder block.

A dummy head 100 includes: a body 110 having a plurality of machining through-holes 111 formed in portions corresponding to cylinder bores 201, and a plurality of bolt insertion holes 112 in which bolts 120 are inserted; through-holes 115 communicating with the bolt insertion holes 112, and collar members 114 disposed at positions in contact with seat faces 121 of the bolts 120. The collar member 114 is made of a material lower in Young's modulus than the body 110. In fastening the bolt 120, an axial force of the bolt 120 is applied to a cylinder block 200 via the collar member 114, thereby dispersing the contact pressure to be applied to the cylinder block 200.