An exhaust device for an engine cam include a flow rectifying device for rectifying a flow of an exhaust gas. The flow rectifying device is disposed in an upstream end of an inner pipe, and comprises protrusions projecting inwardly. The exhaust gas engaging the flow rectifying device has passed through a curved portion of the inner pipe. The inner pipe also includes a muffler having a plurality of vent holes disposed in an inner portion thereof, and an outer pipe surrounding the inner pipe, defining an angular chamber therebetween.