Internal combustion engine

An internal combustion engine, comprising:

• a fan cover that covers a cooling fan driven by a crankshaft;
• a top cover that covers the fan cover;
• and
• a cooling air passage between the fan cover and the top cover, wherein
• the top cover includes an upper surface that is substantially flat and a side surface that extends obliquely downward from a periphery of the upper surface, the side surface is provided with a cooling air side surface intake port, the cooling air side surface intake port includes a plurality of holes that take in cooling air,
• the fan cover includes a first rib facing the top cover in the cooling air passage,
• the fan cover is formed with an inlet opening for taking in the cooling air,
• the first rib is provided over substantially the entire circumference of the inlet opening at a peripheral edge of the inlet opening,
• a back surface side of the top cover is provided with a second rib extending downward in a vertical direction of the internal combustion engine, and
• the second rib and the first rib face each other in a horizontal direction of the internal combustion engine.