The churning type of grease of a viscosity of 15-20 mm²/s and a worked penetration of 200230 is disposed at the rolling surface of the race portions and the channeling type of grease of 2535 mm²/s and a worked penetration of 240270 is disposed at the retainer. By constituting as such, at rotation of the ball bearing, maintaining the lubricant oil film in the bearing the lubrication can be continued, and at non-rotation of the ball bearing the lubricant oil film is protected by the grease to prevent fretting.