An improved air compressor generally includes a cylinder (2) fitted with apiston body (14), a main frame (11) for mounting a motor (12), and an air storage container (3). The cylinder (2), which defines a plurality of exit holes (4, 5, 6) (42, 52, 62), is formed integrally with the main frame (11). The compressed air produced in the cylinder (2) can quickly enter the air storage container (3) via the exit holes (4, 5, 6) (42, 52, 62), so that the piston body (14) can conduct reciprocating motion more smoothly and thus the performance of the air compressor can be increased.
