A throttle opening detection apparatus can include a throttle pipe, a throttle sensor, a resisting force application unit, and a cancel switch. The throttle pipe is configured to partly project into a case fixed to a bar handle and is configured to support rotation at an end portion of the bar handle. The throttle sensor is configured to detect a rotating operation amount of a throttle grip, which is mounted against relative rotation on the throttle pipe, in response to the rotation of the throttle pipe. The throttle sensor is disposed at a fixed position in the case. The resisting force application unit is configured to apply a resisting force to the rotating operation of the throttle grip. The resisting force application unit is accommodated in the case. The cancel switch configured to cancel operation of an auto-cruise controlling apparatus. The cancel switch is accommodated in the case together with the throttle sensor and the resisting force application unit.