An open deck type cylinder block (10) that is one embodiment of the present invention is configured as follows. A shallow portion (21) and a deep portion (22) are provided in a water jacket (20). The shallow portion (21) is provided in a portion that is comparatively far from a head bolt hole (17), while on the other hand the deep portion (22) is provided in a portion that is comparatively close to the head bolt hole (17). A hollow portion (18) in which a block outer wall is hollowed toward a cylinder center side is provided between a bottom wall portion of the shallow portion (21) and a skirt portion (14) used as a crank case.