The utility model relates to a directly connected air compressor, comprising an air reservoir, an air compressor head and an engine. The driving mode of the air compressor head and the engine is direct drive, that is to say the crankcase end cover of the air compressor head is fixed on the box body of the engine. The air compressor head directly drives the crankshaft of the air compressor head to operate through the output shaft of the engine. Additionally, the air compressor also comprises two bottoms and barrel wheels at both sides which are respectively installed in front and rear end of the bottom of the air reservoir, a handle which is provided with at the rear part of the air reservoir and a lengthened handle which is dismountable and is connected on the handle. The fan in the engine positions at the position where the fan can cool down the cylinder of the engine and the air compressor head simultaneously. The output shaft of the engine of the utility model drives the crankshaft of the air compressor head to operate and work, which makes the air compressor head and the engine synthesize into a whole. The directly connected air compressor has the advantages of compact structure, small volume, light weight, long service life, safe and reliable running and convenient operation, maintenance and carry, in particular to be used in the condition of field operation, frequent movement or discommodious electric force supply.