A lubrication device for a dry-sump, four-stroke engine includes a crankcase having a divider wall interposed between a crank chamber and a separate adjoining chamber. A crankshaft is housed in the crank chamber and is driven by reciprocating movement of pistons. A crank web faces the divider wall, which has a through hole for connecting the crank chamber with the separate chamber, and is opened by the crank web when the piston moves from a top dead center position toward a bottom dead center position, and is closed when the piston moves from the bottom dead center toward the top dead center position. A return hole connects the crank chamber and the separate chamber, for returning lubricant oil that flowed through the through hole into the separate chamber from the crank chamber, back to the crank chamber by utilizing pressure fluctuations within the crank chamber.