To provide a vehicular lamp lighting state determination apparatus which has high determination accuracy, dispenses with a drive current detection circuit for lamp lighting control, and does not restrict vehicle structure or vehicle design.

The vehicular lamp lighting state determination apparatus includes: a lamp housed within a lamp housing; a light detection means provided inside a car body; a light guide means which guides light emitted by the lamp from the inside of the lamp housing to the inside of a detection range of the light detection means; and a determination means which determines a lighting state of the lamp on the basis of light guided by the light guide means and detected by the light detection means. According to the determination apparatus, since the lighting state is determined on the basis of light detected by the light detection means inside the car body, a detection circuit for a drive current in lamp lighting control is not required, and a vehicle structure or vehicle design is not restricted. Furthermore, since the lighting state is determined on the basis of light inside the car body, high determination accuracy is achieved without being affected by car body outside environments (external light, weather, car body dirt and the like).