An inflator includes a box and a compressor unit installed in the box. The box is composed of a cover and a base, which are respectively provided with upper and lower airflow-guiding members, which can quickly guide the air current generated by a cooling fan of the compressor unit to enter the motor's housing via two openings of the housing and to flow out of the motor's housing via downstream through holes of the housing, thus dissipating the heat generated by a rotor assembly in the motor, so that heat is not easy to accumulate in the motor, so that maximum power output of the motor can be achieved, and the performance and service life of the motor can be increased.