A bicycle head cap unit is configured and arranged to mount an electrical device or part in a steerer tube of a bicycle fork. The bicycle head cap unit basically has a cap portion and a housing portion. The cap portion is dimension to close a top opening of a steerer tube of a bicycle fork. The housing portion is coupled to the cap portion. The housing portion is configured to form an electrical part receiving space that is located within the steerer tube when the cap portion closes the top opening of the steerer tube of the bicycle fork.