A depressurization device is mounted on a camshaft that includes an exhaust cam operable to push an exhaust rocker arm. The depressurization device includes a base disc mounted on the camshaft and adjacent to the exhaust cam, a counterweight swing arm coupled to the base disc, an elastic element arranged between the base disc and the counterweight swing arm, a depressurization cam element coupled to the exhaust cam and drivable by the counterweight swing arm, and an axle bar extending through the base disc and the counterweight swing arm. The depressurization cam element includes a driving section, a depressurization cam section, and a rotary shaft section. The depressurization cam element is drivable by the counterweight swing arm to rotate by an angle. The depressurization cam section includes an arc portion and first and second cut-off portions arranged at a side opposite to the arc portion.