A positioning device includes a shaft tube having a receptacle receiving a support member that includes first and second ends spaced along an axis. The support member further includes a through-hole extending from the first end through the second end. A bearing is received in the receptacle and includes an end facing the first end of the support member. The end of the bearing includes an inclined pressing surface aligned with a support portion formed on the first end of the support member. The pressing surface deforms the support portion when the bearing is pushed downward during assembly. The deformed support is received in a groove between the pressing surface and an inner periphery of the receptacle to offset and absorb the downward pressing force. The bearing is, thus, reliably fixed in the desired assembly position while preventing the support member from being damaged or generating noise during operation.