To reduce the size of an oil collecting part and lower an output performance requested for a drainage pump.

This blow-by gas reduction device of a dry sump type engine comprises an oil tank 50 storing lubricating oil 52, a feed pump 58 feeding the lubricating oil in the oil tank to an engine 10, a main drainage pump 64 returning the lubricating oil in the crankcase 16 of the engine to the oil tank together with blow-by gas, a sub drainage pump 68 returning the lubricating oil in the cylinder head 14 of the engine to the oil tank, a circulation passage 70 circulating the blow-by gas in the oil tank to the intake pipe 44 of the engine, and a fresh air passage 74 leading fresh air into the cylinder head 14 of the engine through the intake pipe on the downstream side of the connection part of the circulation passage. The discharge rate of the main drainage pump 64 is higher than that of the sub drainage pump 68, and the total discharge rate of the pumps 64 and 68 is higher than that of the feed pump 58.