A power tool including: a motor; an output shaft; a power transmission unit that is configured to transmit rotational power of the motor to the output shaft, wherein the power transmission unit is configured to decrease a rotation speed, which is related with the rotational power, in accordance with a speed reduction ratio that can be changed; a gear shift actuator configured to change the speed reduction ratio of the power transmission unit; a torque detector that is configured to detect a load torque applied to the output shaft; and a control unit that is configured to control the gear shift actuator to change the speed reduction ratio of the power transmission unit in accordance with the detected load torque, wherein the control unit is configured to perform a control to increase the speed reduction ratio of the power transmission unit if the detected load torque reaches a first threshold, the power tool being characterized in that: the control unit is configured to stop driving the motor if the detected torque reaches a second threshold, which is set to detect locking of the motor, during a predetermined period after a control is performed on the power transmission unit to increase the speed reduction ratio; and the control unit is configured to continue driving the motor when the detected load torque does not reach the second threshold during the predetermined period. a motor; an output shaft; a power transmission unit that is configured to transmit rotational power of the motor to the output shaft, wherein the power transmission unit is configured to decrease a rotation speed, which is related with the rotational power, in accordance with a speed reduction ratio that can be changed; a gear shift actuator configured to change the speed reduction ratio of the power transmission unit; a torque detector that is configured to detect a load torque applied to the output shaft; and a control unit that is configured to control the gear shift actuator to change the speed reduction ratio of the power transmission unit in accordance with the detected load torque, wherein the control unit is configured to perform a control to increase the speed reduction ratio of the power transmission unit if the detected load torque reaches a first threshold, the power tool being characterized in that: the control unit is configured to stop driving the motor if the detected torque reaches a second threshold, which is set to detect locking of the motor, during a predetermined period after a control is performed on the power transmission unit to increase the speed reduction ratio; and the control unit is configured to continue driving the motor when the detected load torque does not reach the second threshold during the predetermined period. the control unit is configured to stop driving the motor if the detected torque reaches a second threshold, which is set to detect locking of the motor, during a predetermined period after a control is performed on the power transmission unit to increase the speed reduction ratio; and the control unit is configured to continue driving the motor when the detected load torque does not reach the second threshold during the predetermined period.