Gas bearing device and turbocharger

A gas bearing device for rotatably supporting a rotational shaft by using a gas as a working fluid, comprising:

• 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 penetrates the housing, and configured to restrict movement of the back spring in an axial direction of the rotational shaft,
• wherein an inner peripheral surface of each of the pair of snap rings has self-lubricating properties,
• wherein each snap ring has two end portions and a split between the portions, is formed such that an outer circumference and an inner circumference are concentrically disposed, and has holes in both end portions of each of the pair of snap rings, and
• wherein each snap ring supports the rotational shaft during low-speed rotation of the rotational shaft and a gas film is formed between the rotational shaft and the top foil during high-speed rotation of the rotational shaft.