The present invention relates to an adjustable wrench. The adjustable wrench comprises a handle part, a curved jaw part, a linkage part, an adjusting element and a restoring element. The handle part comprises a toothed portion. The curved jaw part is pivotally connected to the handle part. When the adjusting element is pushed by an external force, the adjusting element further moves the linkage part simultaneously, and the linkage part pulls the curved jaw part to rotate so as to adjust a size of an opening between the curved jaw part and the toothed portion. Accordingly, the present invention has advantages and effects of fast and simple adjustment for use and a lever arm thereof being adjustable for labor saving, etc.