The lubrication structure of an engine is provided with a crankcase having a crank chamber that houses a crankshaft. A first oil reservoir is in communication with the crank chamber and is formed adjacent a bottom of the crank chamber. A second oil reservoir is in communication with the first oil reservoir and is formed adjacent the side of and on the bottom of the first oil reservoir. A reed valve extends diagonally from the bottom of the first oil reservoir toward the top of the second oil reservoir in an opening where the first oil reservoir and the second oil reservoir communicate with the crankcase. The reed valve includes a valve element that opens and closes according to the variation of pressure in the crank chamber. The valve element of the reed valve is arranged on the side of the second oil reservoir.