Auxiliary box gear detection device of speed changer

The utility model provides an auxiliary box gear detection device of a speed changer. An auxiliary gear signal is transmitted to a signal switch through a step of an auxiliary box gear shifting fork or a step of an auxiliary box shifting fork shaft, and the signal switch is arranged on the side face of a shell body of a rear cover and is below a plane of the biggest outline of the speed changer, and the step which is arranged on the auxiliary box shifting fork or the auxiliary box shifting fork shaft pushes the signal switch of an auxiliary box. Therefore, a gear shifting signal is transmitted to the signal switch through the auxiliary shifting fork or the auxiliary box shifting fork shaft, so that a driver is guided.