A rotary shaft support structure supports each of both ends of a rotary shaft passing through a center of a gas turbine and includes a main body arranged around a circumference of the rotary shaft and mounted to each of a compressor casing and a turbine casing of the gas turbine; a pad member disposed between the main body and the circumferential surface of the rotary shaft and biased against the circumferential surface of the rotary shaft for supporting the rotary shaft; a pivot protrusion protruding from the pad member toward the main body; and a pivot housing for receiving the pivot protrusion to rotatably support the pad member. The mechanical bias is supplied by a spring member seated in the mounting groove to bias the pivot housing against the pivot protrusion. The rotary shaft support structure exhibits performance as a bearing by absorbing some of an applied load.