A wrench has a first segment and a second segment pivotally coupled together. The second segment is selectively positionable at various fixed pivotal positions relative to the first segment. The first and the second segments engage with a locking device. The first segment has a first joining end forming a first positioning surface and a second positioning surface. The locking device includes a catch selectively engagable and disengagable from the first and the second positioning surfaces. The catch has a body section abutting against the first positioning surface in a direction radial to the axis of rotation when the first segment is at a first fixed pivotal position relative to the second segment. The first body section is abutted against the second positioning surface in a direction radial to the axis of rotation when the first segment is at a second fixed pivotal position relative to the second segment.