Provided is a saddle-riding-type vehicle exhaust device in which two oxygen sensors that make it possible to detect the deterioration of a catalyst device are provided in favorable positions. A saddle-riding-type vehicle exhaust device 20 having a pipe section 19 that passes below an engine E, guides discharged gas to the rear of the vehicle chassis, and houses a catalyst device C, and also having a muffler 26 connected to the rear end of the pipe section 19, wherein the pipe section 19 is provided with an upstream-side oxygen sensor U positioned on the upstream side of the catalyst device C and a downstream-side oxygen sensor D positioned on the downstream side of the catalyst device C. The pipe section 19 is further provided with an increased-diameter section 61, the diameter of which is increased in order to accommodate the catalyst device C. The downstream-side oxygen sensor D is provided in the increased-diameter section 61. When seen from a chassis-side planar view, the upstream-side oxygen sensor U and the downstream-side oxygen sensor D are located above the center-line Oc of the increased-diameter section 61 in the chassis. The increased-diameter section 61 is positioned below the cylinder block 43 of the engine E and to the front of the crankcase 52.