Disclosed is a fluid dynamic bearing device in which it is possible to prevent detachment of the shaft member reliably and at low cost without involving any increase in the device size. In a thrust bearing portion T, the lower end surface of the shaft member is held in contact with a thrust plate, and the shaft member is rotatably supported in the thrust direction. Protrusions extending radially inwards are provided on a sealing portion attached to an opening of the housing, and these protrusions are engaged with a small diameter portion formed on the outer peripheral surface of the shaft member, thereby preventing the shaft member from coming off.