A biometric information processing device (1) includes a brain wave detecting unit (10), a control unit (20), and a movement assisting unit (30). The brain wave detecting unit (10) detects biometric information in at least one brain region from among a plurality of brain regions that are selectable in accordance with a body part that is a target of function recovery or function improvement. The control unit (20) determines, based on the detected biometric information, at least one activity state in the brain including the location of the brain region(s) that is (are) activated in a subject while attempting to move the body part, and an activation level of such activated brain region(s). When the control unit (20) determines that the at least one activated state of the brain satisfies a predetermined condition, the movement assisting unit (30) executes a predetermined motion to assist movement of the body part.