PURPOSE: To provide a rotary shaft supporting device, which can cope with the rotation of a wide rotation area from a low speed rotation area to a high speed rotation area.

CONSTITUTION: A rotary shaft supporting device is formed with a housing 12, a static pressure bearing 2 supported by the housing 12, a rotary shaft 1, of which both ends are formed with taper parts 1c to be contracted toward the ends and of which central part is supported by the static pressure bearing 2, and taper holes 4a to be fitted out of the taper parts 1c of the rotary shaft 1. Furthermore, the rotary shaft supporting device is provided with a sleeve 4, which can be moved in the axial direction of the rotary shaft 1, a rolling bearing 5, of which inner wheel is fixed to the periphery of the sleeve 4, and a slider 9, which is connected to the outer wheel of the rolling bearing 5 and of which one end is fixed to the housing 12 and the other end is supported by an annular cylinder 2c, which is formed between the housing 12 and the static pressure bearing 2, freely to move in the axial direction of the rotary shaft 1.