A hand tool, characterised in that it comprises: a handle having two pivot ears at one end thereof, a receiving groove defined between the two pivot ears, a transverse hole defined in one lateral side of the handle, and a longitudinal hole defined in a bottom of the receiving groove and in communication with the transverse hole; a driving head having a connecting portion received in the receiving groove of the handle, and a pivot shaft connecting the driving head to the two pivot ears of the handle, the connecting portion having a plurality of teeth at an outer periphery thereof and arranged in an arc; an engaging assembly disposed in the longitudinal hole of the handle, and having an engaging member and a spring interposed between a bottom of the longitudinal hole and the engaging member; the engaging member being characterized by having an engaging tooth at a top thereof for engagement with the teeth of the driving head, and having an arc-shape pushing groove defined in a lateral side of the engaging member and corresponding to the transverse hole of the handle, the arc-shape pushing groove having an arc-shape wall thereof, the arc-shape wall of the engaging member is concaved toward the direction of the spring from the lateral side of the engaging member; and a button movably disposed in the transverse hole of the handle, and having an abutting portion slidably inserted in the arc-shape pushing groove of the engaging member, the abutting portion of the button having an arc-shape plane abutting against the arc-shape wall of the engaging member such that horizontal movement of the button drives the engaging member to move longitudinally along the longitudinal hole of the handle, when the button is pushed toward the engaging member, the engaging member moves to compress the spring in the longitudinal hole of the handle and the engaging tooth of the engaging member is lowered to be disengaged from the teeth of the engaging member. a handle having two pivot ears at one end thereof, a receiving groove defined between the two pivot ears, a transverse hole defined in one lateral side of the handle, and a longitudinal hole defined in a bottom of the receiving groove and in communication with the transverse hole; a driving head having a connecting portion received in the receiving groove of the handle, and a pivot shaft connecting the driving head to the two pivot ears of the handle, the connecting portion having a plurality of teeth at an outer periphery thereof and arranged in an arc; an engaging assembly disposed in the longitudinal hole of the handle, and having an engaging member and a spring interposed between a bottom of the longitudinal hole and the engaging member; the engaging member being characterized by having an engaging tooth at a top thereof for engagement with the teeth of the driving head, and having an arc-shape pushing groove defined in a lateral side of the engaging member and corresponding to the transverse hole of the handle, the arc-shape pushing groove having an arc-shape wall thereof, the arc-shape wall of the engaging member is concaved toward the direction of the spring from the lateral side of the engaging member; and a button movably disposed in the transverse hole of the handle, and having an abutting portion slidably inserted in the arc-shape pushing groove of the engaging member, the abutting portion of the button having an arc-shape plane abutting against the arc-shape wall of the engaging member such that horizontal movement of the button drives the engaging member to move longitudinally along the longitudinal hole of the handle, when the button is pushed toward the engaging member, the engaging member moves to compress the spring in the longitudinal hole of the handle and the engaging tooth of the engaging member is lowered to be disengaged from the teeth of the engaging member.