PURPOSE: To obtain a brain stem training device high in a safety by forming a base face at an upper part of a floating body having a buoyancy capable of floating on a water with one person mounted and easily rolling when the center of gravity of a weight substantially equal to a person on the base face is deviated from the axis of the floatation of the floating body.

CONSTITUTION: A floating body 1 has the buoyancy enough for floating on the water with a person mounted thereon and is constituted so as to easily roll unstably. Since a trainee mounted on the base face 1a of the floating body 1 floated on a sea or a pool falls from the floating body if the center of gravity is not moved against the irregulate oscillation generated when the floating body 1 receives wave or wind at the time of deviating the center of gravity of the body from the axis of the floatation of the floating body 1, he is constantly under tension and forms a state strongly exhibiting the function of the brain stem of the center for sustaining life. Accordingly, this device is used for training a person by placing himself an rolling footing for a time thence repeating and the brain stem of the user is thus stimulated and activated.