A floating bush bearing device, comprising: a casing including a bearing hole; a rotary shaft disposed rotatably inside the bearing hole; a floating bush disposed rotatably inside the bearing hole and surrounding the rotary shaft; an oil-feed hole of lubricant oil, the oil-feed hole having an opening on an inner peripheral surface of the bearing hole; a plurality of communication holes formed on the floating bush, each of the communication holes extending between an inner peripheral surface and an outer peripheral surface of the floating bush, and disposed at intervals in a circumferential direction of the floating bush; and a circumferential groove formed on the outer peripheral surface of the floating bush and extending over an entire circumference of the outer peripheral surface of the floating bush, the circumferential groove passing through openings of the plurality of communication holes, wherein the circumferential groove has a cross-sectional area which varies in accordance with a circumferential position, and wherein a cross-sectional area of a downstream region of the circumferential groove joined to a downstream side of the communication hole in a rotational direction of the floating bush increases toward the communication hole in the circumferential direction of the floating bush, characterized in that a bottom surface of the downstream region joined to the communication hole is formed by an inclined surface inclined from the outer peripheral surface, and wherein the inclined surface is inclined so that the depth of the circumferential groove increases toward the communication hole in the circumferential direction of the floating bush. a casing including a bearing hole; a rotary shaft disposed rotatably inside the bearing hole; a floating bush disposed rotatably inside the bearing hole and surrounding the rotary shaft; an oil-feed hole of lubricant oil, the oil-feed hole having an opening on an inner peripheral surface of the bearing hole; a plurality of communication holes formed on the floating bush, each of the communication holes extending between an inner peripheral surface and an outer peripheral surface of the floating bush, and disposed at intervals in a circumferential direction of the floating bush; and a circumferential groove formed on the outer peripheral surface of the floating bush and extending over an entire circumference of the outer peripheral surface of the floating bush, the circumferential groove passing through openings of the plurality of communication holes, wherein the circumferential groove has a cross-sectional area which varies in accordance with a circumferential position, and wherein a cross-sectional area of a downstream region of the circumferential groove joined to a downstream side of the communication hole in a rotational direction of the floating bush increases toward the communication hole in the circumferential direction of the floating bush, characterized in that a bottom surface of the downstream region joined to the communication hole is formed by an inclined surface inclined from the outer peripheral surface, and wherein the inclined surface is inclined so that the depth of the circumferential groove increases toward the communication hole in the circumferential direction of the floating bush.