PROBLEM TO BE SOLVED: To provide a muscle power balance determination device, a muscle power balance determination method, a balance adjustment system, and a balance adjustment method, capable of measuring balance of left and right muscle forces, and clearly grasping balance abnormality.SOLUTION: Muscle power balance determination devices 1, 101 arranged in a bilaterally symmetrical state, for pressing respective left and right parts of a human body in lateral parallel directions, in directions being almost parallel and almost equal, or in directions being almost equal, comprise: a left elbow front-and-rear part press part 13L and a right elbow front-and-rear part press part 13R for pressing elbows in a state in which, a range from shoulders to elbows lowers almost rearward and a user is in a seating position, and hands are bent forward a user, from positions which are rear sides of the abdomen side parts toward a dorsoventral direction; a left elbow vertical press part 11L and a right elbow vertical press pa
