Floating bush bearing device and supercharger provided with the same

A floating-bush bearing device (1) for rotatably supporting a rotational shaft (2), includes: a floating bush (3) having a cylindrical shape and including a bearing hole (33) into which the rotational shaft (2) is to be inserted; and a bearing housing (4) which rotatably houses the floating bush (3). At least one of an inner peripheral surface (31) of the floating bush (3), an outer peripheral surface (32) of the floating bush (3), or an inner peripheral surface (41) of the bearing housing (4) includes, in a cross section in an axial direction thereof, a plurality of land portions (311, 321, 411) having a true arc shape which is a part of a true circular shape, and a plurality of recess portions (312, 322, 412) being disposed at a position recessed from the land portions, the recess portions being configured such that a distance between the recess portions and a virtual true circular line (31a, 32a, 41a) passing through the land portions increases in a direction opposite from a rotational direction of the rotational shaft (2) from end portions (311b, 321b, 411b) of the land portions opposite from the rotational direction of the rotational shaft.