A sensor mounting structure includes a sensor and a sensor receiving section including a receiving lock portion protruding from a seat surface to be locked to a portion of a collar section, wherein the collar section of the sensor includes: a sensor lock portion; and an interference avoiding portion in an overlapping portion of the collar section, wherein when the sensor main body is inserted in the sensor insertion hole in an incorrect pose, the collar section overlaps with the receiving lock portion in the overlapping portion, wherein the incorrect pose is offset from a normal pose around the center axis, wherein in the normal pose, the sensor lock portion is locked to the receiving lock portion, wherein the interference avoiding portion avoids interference of the collar section with the receiving lock portion along a direction of insertion of the sensor main body into the sensor insertion hole.