To provide a simply formed rotation transmission mechanism by engagement capable of maintaining the reduction effect of tooth hitting noise caused between engaged surfaces for a long period by using a grease mixed with a powder.
This rotation transmission mechanism comprises a drive member and a driven member for transmitting a rotation by the engagement. Both engaged surfaces are coated with a lubricating grease. A powder formed of an elastic material is mixed in the lubricating grease. A large number of fine recesses into which the powder is allowed to intrude are formed in the engaged surfaces of the drive member or the driven member.