An air compression device is applied in an air compressor. A rotatable pressure regulating disk and a valve are disposed in a rotor set. When external air enters an air chamber in the rotor set, the air is exhausted after being compressed through rotation of a first rotor and a second rotor. When the two rotors compress the air, a user may control the pressure regulating disk to rotate to advance or postpone exhaust of the air from the valve, so as to change an exhaust pressure in the air chamber to adjust an exhaust volume output by the rotor set. An adjustable air intake disk may further be added, so that timing adjustment can be performed during both air intake and exhaust.