An air compressor is received in an accommodation box and contains a body, a cylinder, a motor, and a transmission mechanism. The body includes a first positioning orifice and a second positioning orifice. The cylinder is connected on the body and communicates with an air storage holder. The motor is fixed on the body, a small gear is received in the first positioning orifice, and a connection seat is accommodated in the first orifice. The transmission mechanism actuates a piston to move in the cylinder reciprocately so as to produce compressed air. The motor includes at least one locking extension for engaging the motor with the body. A first end of a respective one locking extension extends from the motor, and a second end of the respective one locking extension is engaged on the body, hence the motor is fixed on the body securely without using any screws.