The invention discloses an adjusting device. The adjusting device comprises a body, an adjusting inner gear ring and an adjusting shaft. A cavity is formed in the body. A first hole and a second holeare formed in the first end of the body. A third hole is formed in the peripheral wall of the body. The first hole, the second hole and the third hole communicate with the cavity. The adjusting innergear ring is matched in the cavity. A plurality of adjusting holes penetrating through the peripheral wall of the adjusting inner gear ring are formed in the peripheral wall of the adjusting inner gear ring. The cross sectional areas of the plurality of adjusting holes are different from each other. The second end of the adjusting shaft is provided with an adjusting gear, penetrates through the second hole and extends into the cavity. The adjusting gear is meshed with the adjusting inner gear ring. The adjusting shaft can rotate to drive the adjusting inner gear ring to rotate, so that the third hole can communicate with the cavity through one of the plurality of adjusting holes. The adjusting device can be used for adjusting the hardness of a shock absorber and is wide in adjusting rangeand good in adjusting effect.