Air compressor

An air compressor comprising:

• a base including multiple positioning orifices, one of which accommodates a bearing;
• a cylinder connected on the base and including an air storage seat communicating on the cylinder;
• and
• a transmission mechanism driving a piston to reciprocately move in the cylinder, thus compressing air;
• wherein the transmission mechanism including a torque gear and a central orifice defined on the torque gear, and the transmission mechanism further including a connection rod extending from the torque gear, wherein the central orifice has screw threads formed therein, and the central orifice of the torque gear corresponds to the bearing in the one positioning orifice of the base, and a screw bolt is screwed with the central orifice after being inserted through the bearing and the torque gear, thus connecting the transmission mechanism automatedly;
• wherein the connection rod of the torque gear is rotatably connected with the piston.