Blocking apparatus, as well as a gearbox drive unit containing such a blocking apparatus, as well as a method for production of a gearbox drive unit such as this for blocking any rotary movement of a shaft (14) with respect to a housing (16) of a gearbox drive unit (10), having a first blocking element (32) and having a second blocking element (34) which can be moved axially with respect to the first blocking element (32) by means of an electromagnet (44) and at least one return element (42), in order to produce a connection between the first blocking element (32) and the second blocking element (34) such that they cannot rotate with respect to one another, with the electromagnet (44) having an inner pole (47) which is surrounded by an electrical coil (45), and with the inner pole (47) having an axial projection (51) which engages in a corresponding opening (64) in the second blocking element (34), for axial guidance and centering.