A driving device for an air compressor includes a base, a motor, a main gear, a subordinate gear, a shaft, a weight, and a driving arm combined with an air cylinder and a cylindrical member. When the motor is electrified, the main and the subordinate gear are rotated, with the subordinate gear rotating the shaft, which then rotates the weight. The weight then rotates centrifugally to let a first end of the driving arm rotate and then the piston formed the second end of the driving arm is moved to reciprocate back and forth in the cylindrical member to produce compressed air to flow out for use.