1. A labeling apparatus comprising: means for inputting a binary image data through raster scanning; means for assigning a temporary label to a target image of a first scan line on the basis of a data pattern formed by four binary image data which include the target image, an adjacent image following the target image in the first scan line and two images in a next scan line adjacent to said two images in the first scan line; and means for unifying the temporary label with another temporary label obtained by said assigning means.