A decelerator is disclosed. The decelerator according to an embodiment of the present invention includes an input shaft in which a first sun gear and a second sun gear are installed and which is inputted with rotation from the outside; a first differential gear receiving a rotatory force by being engaged with the first sun gear and installed on a first fixing pin to be able to rotate; a second differential gear receiving the rotatory force by being engaged with the first differential gear and installed in a second fixing pin to be able to rotate; a fixing ring gear engaged with the second differential gear and fixed to the inside of a housing; a differential carrier in which the first fixing pin and the second fixing pin are installed in order for the first differential gear and the second differential gear to rotate on the axis and revolving around the input shaft and installed in the input shaft to be able to rotate; a decelerator ring gear rotating with the differential carrier by being installed at the rear end of the differential carrier; and a planet gear member connected to an output shaft and decelerating and rotating due to the different rotatory force by receiving the different rotatory force from the second sun gear and the deceleration ring gear. [Reference numerals] (100) Input part; (200) Retardation part; (300) Junction part
