Provided is a projection optical system including a first part which projects an image; a second part having an image forming device which forms an image using a light and emits the image to the first part, and having an axis angled toward an axis of the first part; a third part including at least one light source, which emits the light, and having an axis angled toward the axis of the second part; and a deflector which guides the light emitted from the third part toward the second part, wherein a pupil plane of the second part is located between the first part and the second part, and a cross-point between the axis of the first part and the pupil plane of the second part is separated from a cross-point between the axis of the second part and the pupil plane of the second part.