INTERNAL COMBUSTION ENGINE AND STRADDLED VEHICLE

An internal combustion engine (10) includes: a first side wall (21) that partitions the inside of a crank case (11) into a first chamber (31) and a second chamber (32); an oil pan (25) provided on a bottom portion of the first chamber (31); an oil tank (33) formed in the second chamber (32); a scavenge pump (40) having an intake port (41) that communicates with the oil pan (25) and a discharge port (42) that communicates with the oil tank (33); and a feed pump (50) having an intake port (51) that communicates with the oil tank (33). An oil return hole (63) that connects together the oil tank (33) and the first chamber (31) is formed in an upper portion of the first side wall (21).