The invention relates to a switching device of motor machine, comprising: a fixed contact element fixedly arranged in a casing; a movable contact bridge for related jointing the fixed contact element; a movable contact bearing element bearing the contact bridge; and an electromagnet acted upon the contact bearing element. The electromagnet comprises a coil frame fixed on the casing; an armature movably coupled with the contact bearing element; a yoke acted together with the armature; and a fixed device joggled on the yoke and the coil frame to fix the yoke on the coil frame.