A lubrication structure for a bearing section of an internal combustion engine including a crankcase having a wall portion, a bearing secured to the wall portion, a rotational shaft supported for rotation by the bearing, and a bearing restriction member disposed on a side face of an outer race portion of the bearing and configured to suppress coming off of the bearing, wherein an oil receiving portion formed in a swollen state on the wall portion along an outer periphery on the outer side of an outer periphery below the center axis of the bearing, and an oil reserve section is provided so as to extend over the oil receiving portion and the bearing restriction member.