A simple open-end wrench includes a driving head including first and second jaws, a space delimited between the first and second jaws, first and second recesses extended from the space, a pawl pivotally embedded in the first recess, and a biasing mechanism received in the second recess and abutted against the pawl. The pawl includes an abutting end disposed outside the second recess and extended into the space. The pawl is pivotal to a position with the abutting end thereof disposed within the second recess.