ROTARY SUPPORTING DEVICE

PROBLEM TO BE SOLVED: To provide a structure capable of reducing torque of each ball bearing 3, 3 sufficiently, ensuring a sufficient oil film in a contact part of rolling faces of each ball 9, 9 constituting each ball bearing 3, 3 and each raceway track 4, 6 of an outer ring and an inner ring, and ensuring durability of each contact part sufficiently. SOLUTION: Pre-load load given to each ball bearing 3, 3 is reduced to such extent that gross slip occurs in a contact part of each ball 9, 9 and the raceway track 6 of the inner ring in at least a part of a scope of rotational speed of the inner ring 7 realized when using. At the same time, lubrication conditions of each ball bearing 3, 3 are regulated so as to prevent occurrence of damage and seizure on the rolling faces of each ball 9, 9 and each raceway track 4, 6 of the outer ring and the inner ring during at least desired operation time in the scope of rotational speed at which gross slip occurs. COPYRIGHT: (C)2007,JPO&INPIT