Abstract: A speed adjusting device for a drill includes two pulley assemblies between which a belt is connected. Each pulley assembly has a fixed disk and a movable disk so that an effective diameter that the belt engages the pulley assembly can be changed by adjusting a distance between the disks. One of the pulley assembly driven by a motor shaft has a spring which is biased between the movable disk and a motor. A pressing member presses the movable disk of the other pulley assembly which is connected to an output shaft. A lifting device can be operated to adjust the pressing member to allow the spring to change the distance between the other pulley assembly so as to obtain different effective diameter in each pulley assembly.