PROBLEM TO BE SOLVED: To accurately detect condition change of a muscle part of a body portion when a predetermined body portion is maintained at a constant posture while extending muscle like a stretch exercise.SOLUTION: A muscle condition change detection device concerning the present invention is the device that detects a temporal condition change of a muscle part on the basis of the reaction force upon pressing the muscle part of the body part by the constant force, when a predetermined body part is maintained at a constant posture while extending muscle. The muscle condition change detection device performs such processing that the relationship between the reaction force and the time is linearly approximated about the value obtained by performing logarithmic transformation of the reaction force acquired with time and the time when obtaining each reaction force, and the timing when the straight line is transited to another kind of straight line is estimated to be the timing when the condition of the muscle part is changed.
