Pump structure of internal combustion engine

A pump structure of an internal combustion engine, comprising:

• a main oil pump disposed at a lower portion of the internal combustion engine and configured to suck lubricating oil stored in a bottom portion of a crankcase of the internal combustion engine and feed the lubricating oil to respective parts of the internal combustion engine;
• and
• a scavenge pump disposed at a lower portion of the internal combustion engine and configured to recover the lubricating oil after use from any lubricated part among the respective parts of the internal combustion engine and return the lubricating oil to the inside of the crankcase,
• the scavenge pump comprising:
• an oil suction passage extending from the lubricated part to a suction side of the scavenge pump;
• and an air introduction passage for negative pressure control connected to the oil suction passage at a position between the lubricated part and the suction side of the scavenge pump,
• the air introduction passage having at an end thereof an air introduction port set to a height position such that the air introduction port is open to the inside of the crankcase and such that, when an oil level of the lubricating oil in the bottom portion of the crankcase is inclined, the lubricating oil flows in from the air introduction port and returns from the scavenge pump to the inside of the crankcase.