The present invention relates to a bed to adjust a slope of the bed according to brain waves and a method thereby, to adjust the slope to generate the maximum alpha waves of brain waves which are generated by the change of the blood amount to be provided in a bed user's brain. For this, there is provided a bed to adjust the slope of the bed according to brain waves that an ankles fixing device 14 is mounted at one side of the bed 12 and which is capable of rotating within predetermined angles around a rotation central hinge 18 which is installed at one side of the lower surface of the bed, wherein the bed comprises brain waves detection means 50 which is mounted at another side of the bed 12, and which user is able to put on, separation means for separating alpha waves and beta waves having predetermined frequency range from output signals of the brain waves detection means 50, and adjustment means for adjusting the inclination of the bed 12 so that the maximum alpha waves can be detected based on the alpha waves and the beta waves.