A planetary gear unit including a sun gear rotatable by torque from a drive source, an outer gear disposed coaxially with the sun gear, multiple planetary gears disposed within the outer gear at equal intervals along an inner circumference of the outer gear to engage the sun gear and the outer gear, a carrier pin to rotatably support each of the multiple planetary gears, and a carrier rotatable coaxially with the sun gear and the outer gear to support both ends of the carrier pin. At least a first end of the carrier pin is constructed of a circular portion and a linear portion to form a first supported part. The carrier includes a first support part that supports the first supported part and is formed to position the circular portion of the first supported part downstream from the linear portion in a direction of rotation of the carrier.