A rotatably supporting device for correcting balance of a rotating body includes a journal supporting part having a mandrel that rotatably supports the rotating body in a floating state about a vertical axis, a thrust supporting part that is provided at a lower end portion of the mandrel and supports a bottom part of the rotating body in the floating state, a first fluid supply passage that supplies a fluid for floating between the mandrel and a rotation support hole of the rotating body, an annular groove provided in the thrust supporting part so as to face the bottom part of the rotating body, and a second fluid supply passage that communicates with the annular groove to supply a fluid thereto for floating the rotating body. A rotatably supporting device for correcting balance of a rotating body includes a journal supporting part having a mandrel that rotatably supports the rotating body in a floating state about a vertical axis, a thrust supporting part that is provided at a lower end portion of the mandrel and supports a bottom part of the rotating body in the floating state, and a fluid supply passage that supplies a fluid for floating between the mandrel and a rotation support hole of the rotating body, in which a space part is formed in at least either one of the mandrel and the rotation support hole for widening a space other than at a supporting portion.