Bearing device and rotating machine

A bearing device configured to rotatably support a rotational shaft of a rotating machine, comprising:

• a semi-floating bearing supported by a bearing housing;
• and
• an anti-rotation pin fixed to the bearing housing and having an insertion portion inserted from an outer peripheral side into an insertion hole formed on an outer surface of the semi-floating bearing,
• wherein, in a plan view perpendicular to an axis of the rotational shaft, the insertion portion has an outer surface that extends linearly along a direction perpendicular to an axis of the bearing device, and at least one pin-side protrusion that protrudes toward the other of the insertion hole, wherein the pin-side protrusion includes:
• a first pin-side convex surface portion that protrudes in a convexly curved shape in a plan view perpendicular to the axis of the rotational shaft;
• and a second pin-side convex surface portion that protrudes in a convexly curved shape on an outer peripheral side of the first pin-side convex surface portion in a plan view perpendicular to the axis of the rotational shaft, the second pin-side convexly curved portion being separated from the first pin-side convexly curved portion by the outer surface of the insertion portion.