Sight Device

In a sight device, an objective lens unit is disposed at an end of a housing. An ocular lens unit is disposed at another end of the housing and opposite to the objective lens unit. An erector unit is disposed between the objective lens unit and the ocular lens unit. A adjusting unit is movably disposed on the housing and radially propped against the erector unit to adjust the erector unit. A light emitting unit is disposed on the erector unit and includes a light source for emitting a light beam to an object. A light receiving unit is disposed on the erector unit and includes a light sensor for receiving the light beam reflected by the object. In any cross section of the housing, any point on the external surface of the housing is approximately equally distant from the second central axis.