The typewriter has a powered motor, an electric power switch, a drive shaft driven by the motor, a driven mechanism including printing and carriage return mechanisms connected to the drive shaft by way of respective clutches, and locking device for locking the clutches in their disconnect state. The locking device consist essentially of a cam portion on a manually operable member designed for turning on and off the switch, and a locking element actuated by the cam portion. When the manually operable member is actuated for turning off the switch, the clutches are locked in their disconnect state by the cam portion through the locking member. During cessation of the motor operation, these clutches may not be connected by faulty manipulation of the key or keys associated with the driven mechanism for reliably preventing incidental printing or carriage return movements upon restarting of the motor from occuring.