ROTATION DRIVE DEVICE

Provided is a rotation drive device, which has a driving-force transmission mechanism configured such that a drive transmission member provided on a driving shaft and a disk-shaped driven member attached to a main shaft are directly or indirectly engaged with each other and which is further configured such that an increase in diameter of the driven member due to thermal expansion can be suppressed as much as possible. The driven member includes an inner ring attached to the main shaft, and an outer ring attached to the inner ring by shrinkage fit and having an engaging groove formed to be opened on an outer circumferential surface thereof. The inner ring is formed by a low thermal expansion member, which is an alloy having a thermal expansion coefficient of 5×10−6/K or less. The outer ring is formed of a hardenable iron-based material.