An air compressor includes a supporting base having an arm extended from a plate, and a cylinder housing formed integral with the arm and the plate and having an outlet tube. The cylinder housing includes three or more ducts extended outwardly from the outlet tube and communicating with the outlet tube, for attaching a pressure gauge, a nozzle or other devices. A piston is slidably received in the cylinder housing. A motor is attached to the plate, and includes a spindle extendible through either the lower or the upper portion of the plate, and coupled to the piston with an eccentric member, to move the piston to the cylinder housing in a reciprocating action, in order to generate pressurized air.