A region correction device (1) according to the present disclosure includes: an input unit (41) that receives an input of prediction region information indicating a prediction region (PA) indicating an image of a predetermined subject, the prediction region (PA) being detected from a captured image obtained by imaging the predetermined subject; a line segment extraction unit (42) that extracts a line segment on the basis of a contour of the prediction region (PA) indicated by the prediction region information; a correction unit (43) that corrects the prediction region (PA) on the basis of the line segment; and an output unit (44) that outputs corrected prediction region information indicating a corrected prediction region, the corrected prediction region being the prediction region (PA) that has been corrected.