To provide a region extracting device for stably extracting an object region, even if patterns and noise exist in the object region, and to provide a region extracting method.

The device comprises a two-dimensional and time sequential data acquiring means 101; a region-of-interest (ROI) setting means 102 for setting an ROI relative to a two-dimensional data configuration region; an observation probability density calculating means 103 for calculating feature information of the ROI and calculating the probability density of the feature information in the ROI; an object region probability density updating means 104 for updating the object region probability density, based on the calculated probability density and the object region probability density of the feature information in the object region at preceding time; a background region probability density calculating means 105 for calculating the feature information of a background region, based on the feature information of the calculated entire two-dimensional data configuration region and the updated object region probability density; and a region-extracting means 106 for extracting the object region, based on the updated object region probability density and the probability density of the feature information in the background region.