Abstract: Portable electromechanical tool comprising a unit (2) enclosing a continuous current electric motor (23) powered by a storage battery (4), a mechanical reduction gear (25) driven by the output shaft of said motor, which activates a working head (3) by means of a device (40) for converting the rotary motion of the motor (23) into a longitudinal translation movement, which is transmitted to said working head (3). According to the invention, said converting device (40) comprises a planetary roller screw, said screw comprising a threaded part (41), which is driven in rotation by said reduction gear to transmit motion via planetary rollers (43) to a threaded nut (42) that drives a mobile part (5) of said working head (3) in translation.