An obstacle detecting unit includes a reflective mirror formed to reflect light which is incident from a front area and a lower portion of the front area below a central portion of the reflective mirror; a catadioptric lens disposed coaxially with the reflective mirror in an upper portion of the reflective mirror, the catadioptric lens on which light incident from the front area and an upper portion of the front area; and an image forming module disposed coaxially with the reflective mirror below the reflective mirror, the image forming module on which the light reflected by the reflective mirror is incident, wherein a through hole is formed in the central portion of the reflective mirror, and the light coming out of the catadioptric lens passes through the through hole and then is incident on the image forming module.