An exhaust flow rate control valve includes an on-off valve which is switched between a closed state in which a flow passage area of an exhaust pipe is decreased, and an opened state in which the flow passage area is increased. A notch is formed in the on-off valve, and a recess is formed in an inner pipe member of the exhaust pipe to correspond to the notch. A resilient member, for biasing the on-off valve in a closing direction, is disposed in a space formed between the recess and an outer pipe member of the exhaust pipe. Thus, the degree of freedom is improved in setting the operating characteristic of the on-off valve, without increasing the size of an exhaust structure.