Provided is a planetary geared reducer with a dual reduction ratio. The reducer includes: a housing provided with a ring gear, and having one side where an input shaft is rotatably inserted and an opposite side where an output shaft is rotatably inserted; a sun gear provided at the input shaft; at least one planetary gear engaged between the sun gear and the ring gear; and a high reduction carrier provided at the output shaft to rotatably support the planetary gear by a rotation pin, wherein the high reduction carrier is coupled with a low reduction carrier, the low reduction carrier has a through-hole where the sun gear passes, the through-hole has a low reduction gear engaged with the sun gear, and the sun gear is selectively interlocked with the planetary or low reduction gear according to a forward or rearward movement of the input shaft to perform dual reduction.