An exhaust mixing device for mixing an exhaust produced by an engine with a reagent exhaust treatment fluid that is dosed into the exhaust from a dosing module. The sliding bearing comprises a sleeve, a shaft enclosed in said sleeve, and, a cap fitted into the sleeve, the sleeve having a shouldered hole with a first shoulder on which the cap is held, wherein the internal circumferential surface of the sleeve or the external circumferential surface of the cap includes a second shoulder circumferentially formed thereon. Thereby, the spot size of the light incident on the optical fiber on the reception side is changed while maintaining the light propagating between the first optical fiber and the second optical fiber point-symmetric in mode field shape. A first contact means 20a is provided on the throttle body 1 and the relief lever 9 and the throttle body 1 contacts the relief lever 9 when the relief lever 9 pivots to a predetermined pivot position B in the valve closing direction.