A supercharger includes a first introduction part having a first flow channel; a second introduction part having a second flow channel; a chamber into which the exhaust gas is introduced; an outlet part having one or a plurality of outlet flow channels; and a valve member housed in the chamber. The chamber has a first introduction port that leads to the first flow channel, a second introduction port that leads to the second flow channel, and one or a plurality of outlet ports that lead to the outlet flow channel. A main circulation space is secured. The valve member is capable of opening or closing, and allows two or more opened ports among the first introduction port, the second introduction port, and the outlet port to communicate with each other through the main circulation space.