A clearance δ between an inner peripheral surface of an attachment hole of an attachment tongue and an outer peripheral surface of a valve shaft is set to be smaller than an allowable displacement amount λ in an axial direction of a valve with respect to the attachment tongue. When a condition is satisfied in which the outer peripheral surface of the valve shaft comes into contact with a front-side periphery and a back-side periphery of the attachment hole of the attachment tongue, and in which a top surface of a valve body comes into contact with a back surface of the attachment tongue, a waste gate valve is constituted so that a metal washer becomes non-contact with a front surface of the attachment tongue.