According to an embodiment, a processing device includes a generating unit, a detecting unit, and a determining unit. The generating unit is configured to generate two-dimensional distribution information of an object, the two-dimensional distribution information associating between at least a lateral direction distance and a depth direction distance of the object. The detecting unit is configured to detect a continuous area having continuity in a depth direction in the two-dimensional distribution information. The determining unit is configured to determine whether the continuous area represents a detection target.