Actuator apparatus for sliding barrier, comprising an electric motor which is a torque motor operated by a control and command unit and configured to cause the rotation of its output shaft which is provided with a pinion designed to be coupled directly with a linear gear integral with said barrier, said actuator apparatus further comprising a locking device comprising: - at least one bolt engagement member which is mounted on a fixed part of said actuator apparatus , - a locking member acting on the shaft of said torque motor by means of a damping mechanism , - means for moving said bolt engagement member between an engagement position of said locking member and a disengagement position therefrom, said means being configured to automatically bring said engagement member in said engagement position when said torque motor is not powered, wherein: - said locking member is mounted neutral on said shaft of said torque motor , - said damping mechanism is interposed between said shaft of said torque motor and said locking member and comprises at least one body which is integral with the rotation of the output shaft and which is maintained in direct or indirect contact with said locking member , - said locking member comprises a toothed wheel of which at least one tooth is designed to be engaged by a bolt engagement member when said torque motor is not powered, to said bolt engagement member being associated with an electromagnetic actuator of the monostable type which brings it in a disengaged condition from said toothed wheel , when it is powered, and it allows the elastic reaction of at least one elastic element to bring it into a engaged condition when it is not powered, - said damping mechanism comprises at least one friction element which is interposed between the locking member and said body that is integral with the rotation of the output shaft . - at least one bolt engagement member which is mounted on a fixed part of said actuator apparatus , - a locking member acting on the shaft of said torque motor by means of a damping mechanism , - means for moving said bolt engagement member between an engagement position of said locking member and a disengagement position therefrom, said means being configured to automatically bring said engagement member in said engagement position when said torque motor is not powered, - said locking member is mounted neutral on said shaft of said torque motor , - said damping mechanism is interposed between said shaft of said torque motor and said locking member and comprises at least one body which is integral with the rotation of the output shaft and which is maintained in direct or indirect contact with said locking member , - said locking member comprises a toothed wheel of which at least one tooth is designed to be engaged by a bolt engagement member when said torque motor is not powered, to said bolt engagement member being associated with an electromagnetic actuator of the monostable type which brings it in a disengaged condition from said toothed wheel , when it is powered, and it allows the elastic reaction of at least one elastic element to bring it into a engaged condition when it is not powered, - said damping mechanism comprises at least one friction element which is interposed between the locking member and said body that is integral with the rotation of the output shaft . <EOS>