A wrench includes a tool head, an outer tube unit, a rod unit and a sleeve unit. The outer tube unit includes an outer tube, a tail seat and a biasing member. The tail seat is detachably mounted to the outer tube. The rod unit includes an inner rod telescopically disposed in the outer tube and formed with a plurality of cavities. The biasing member biases the inner rod away from the tail seat. The sleeve unit is slidably sleeved on the outer tube and includes a positioning ball engageable with a selected one of the cavities to prevent the inner rod from moving relative to the outer tube and removable from the selected one of the cavities to allow the inner rod to move relative to the outer tube.