A wrench comprises a ratchet device in a ratchet box portion and including a downward bar, a lateral recess having first and second walls, and a bore in communication with the recess; a rotating disc including a shaft extended into the bore, and an actuation member on one side of the shaft; and a locking member in the recess and including an outer ratchet adapted to engage with the ratchet of the handle, an inner groove for receiving and being engaged with the actuation member in the recess, and third and fourth walls at both sides of the groove, either the third or fourth wall being adapted to contact the first or second wall when the locking member pivots to one of left and right positions in the ratchet device. Rotating the rotating disc opposite to the rotation of the handle will switch a direction of exerted force.