The invention relates to an engine brake device with lower manufacture cost, comprising a vent valve control mechanism. The vent valve control mechanism comprises a driving force input cam, a cam driven wheel, a handspike, a rocker arm and a rocker arm shaft, wherein one end of the handspike is connected with one end of the rocker arm, the cam driven wheel is arranged at the other end of the handspike, the driving force input cam is arranged outside the cam driven wheel, a horizontal driving piston and a vertical brake plunger piston are arranged at the other end of the rocker arm, a circular groove is arranged in the middle of the driving piston, one side of the circular groove and one side of the driving piston at the left are used as a non-operation surface and an operation surface to compress and tightly contact with the upper end surface of the brake plunger piston, and a vent valve rod connecting piece is arranged below the brake plunger piston. Engine power is periodically transferred to the rocker arm by the driving force input cam, and a gap between the rocker arm and the vent valve rod connecting piece is controlled by utilizing an electromagnetic valve to switch two states of brake and normal operation, therefore, the size and the weight of the brake device are reduced without high oil pressure or the defects caused by the high oil pressure, such as leakage, deformation and load fluctuation.