In an engine, an oil channel arrangement is formed between an outer periphery of a lower-case setting bolt and inner peripheries of a case-side bolt hole and a block-side bolt hole so as to prevent the flow of foreign matters as contained in lubricating oil flowing from a main gallery toward a crank journal. The oil channel has a cross section that varies between the main gallery and the crank journal so as to decrease the flow velocity of the lubricating oil flowing from the main gallery toward the crank journal. The decreased velocity of oil allows the foreign matter to settle by gravitational force in a collecting space.