The deformation of cylinder bores in a cylinder block is prevented. The cylinder block 19 is inserted into a front housing 11. The cylinder block 19 is fixed to the front housing 11 by tightening plural screws 38 which penetrate through the cylinder block 19, from an end surface 191 side thereof, to be screwed into an end wall 32 of the front housing 11. Plural deformation absorbing grooves 39 are provided on the end surface 191. Each one of the deformation absorbing grooves 39 is provided in each intermediate space between the adjacent paired cylinder bores 41.