In gearshift transmissions, shafts are selectively coupled to loose gears by means of coupling apparatuses in order to shift gears. The coupling apparatuses usually have a body that is connected to the shaft for conjoint rotation. For coupling, the coupling apparatuses typically have a sliding sleeve, which has an inner axial set of teeth, wherein the sliding sleeve is connected to the body for conjoint rotation but in an axially slidable manner. By means of axial sliding of the sliding sleeve, the sliding sleeve is moved onto a coupling segment of the loose gear such that the loose gear and the body are connected for conjoint rotation by means of the sliding sleeve. The problem addressed by the invention is that of proposing an actuator device for shifting a transmission, said actuator device being easy to integrate. This problem is solved by means of an actuator device (1) for a transmission (2) having a shifting sleeve insert (3) for coupling a synchronizing body (23) to a loose gear (22a, b) and having an electric motor (5) for axially sliding the shifting sleeve insert (3), wherein the shifting sleeve insert (3) is arranged coaxial to the electric motor and/or in the electric motor (5).