A throttle sensor mounting structure for suppressing the influence on the arrangement of a lighting device located on the front side of a head pipe. A throttle sensor mounting structure in a saddle seat type vehicle includes a handle, a throttle grip rotatably mounted on the handle, a throttle sensor for detecting an operational amount of the throttle grip, a controller for controlling a power unit according to a detection value from the throttle sensor, a pair of right and left main frames extending to the rear from a head pipe, and a headlight provided on the front side of the head pipe. The throttle sensor is located on the rear side of the head pipe and between the right and left main frames so as to be superimposed on the main frames as viewed in a side elevation.