An auxiliary trip unit for tripping a circuit breaker according to an electric command, comprising: - a drive part associated with a blade (4; 104) that is movable between a neutral position and an active position, - at least one flexible actuating means (6; 106) designed to store mechanical energy when the blade is in its neutral position, and to actuate it from its neutral position to its active position, by means of said energy, with a movement producing a tripping operation of the circuit breaker, following unlatching of the blade (4; 104), - a latch (31; 131) fitted swivelling around a swivelling axis (X 2 -X' 2) and designed to secure the blade (4; 104) in its neutral position, against releasing of said energy, until movement of the latch (31; 131) takes place to a releasing position in which said unlatching takes place, - a first bias spring (33; 133) fitted to bias the latch (31; 131) to a latching position in which the latch (31; 131) secures the blade (4; 104) in its neutral position, - a thrust slide (14, 16; 114, 116) to propel the latch out of its latching position to its released position, - a second bias spring of the slide (14, 16; 114, 116) in a first direction, - an electric coil (7; 107) generating an electromagnetic force to drive the slide (14, 16; 114, 116) against the second bias spring, in a second direction opposite to the first direction, when this coil (7; 107) is supplied by said electric command, characterized in that the latch (31; 131) comprises a nose salient in a direction passing through the swivelling axis (X 2 -X' 2) so as to comprise a salient end where localized latching of the blade (4; 104) takes place when said latch (31; 131) in the latching position secures the blade (4; 104) in the neutral position, and in that said latch (31; 131) is designed to receive a thrust force acting in the direction of resetting of the blade to the latching position. - a drive part associated with a blade (4; 104) that is movable between a neutral position and an active position, - at least one flexible actuating means (6; 106) designed to store mechanical energy when the blade is in its neutral position, and to actuate it from its neutral position to its active position, by means of said energy, with a movement producing a tripping operation of the circuit breaker, following unlatching of the blade (4; 104), - a latch (31; 131) fitted swivelling around a swivelling axis (X 2 -X' 2) and designed to secure the blade (4; 104) in its neutral position, against releasing of said energy, until movement of the latch (31; 131) takes place to a releasing position in which said unlatching takes place, - a first bias spring (33; 133) fitted to bias the latch (31; 131) to a latching position in which the latch (31; 131) secures the blade (4; 104) in its neutral position, - a thrust slide (14, 16; 114, 116) to propel the latch out of its latching position to its released position, - a second bias spring of the slide (14, 16; 114, 116) in a first direction, - an electric coil (7; 107) generating an electromagnetic force to drive the slide (14, 16; 114, 116) against the second bias spring, in a second direction opposite to the first direction, when this coil (7; 107) is supplied by said electric command,