Gas bearing device and turbocharger

A gas bearing device using a gas as a working fluid, comprising:

• a rotational shaft;
• a housing where the rotational shaft penetrates;
• an annular top foil disposed inside the housing and surrounding an outer periphery of the rotational shaft;
• a back spring disposed between the top foil and the housing, and having a plurality of crests contacting the top foil and a plurality of valleys contacting the housing;
• and
• a pair of snap rings fitted in shaft holes where the rotational shaft of the housing penetrates, and configured to restrict movement of the back spring in an axial direction of the rotational shaft,
• wherein the gas bearing device has a turning groove in a region of the rotational shaft facing each of the pair of snap rings,
• wherein the rotational shaft includes a first turning groove on one end side of the rotational shaft and a second turning groove on an opposite end side of the rotational shaft,
• wherein the first turning groove has:
• a first end adjacent to the back spring and the top foil;
• and a second end located on the one end side of the rotational shaft, and the second turning groove has:
• a third end adjacent to the back spring and the top foil;
• and a fourth end located on the opposite end side of the rotational shaft, and
• wherein the first turning groove extends from the first end to the second end in a circumferential direction about an axis of the rotational shaft, which is the same circumferential direction in which the second turning groove extends from the fourth end to the third end.