Decelerator and engine brake with the Same

It is a saucer (100) is disclosed, in which a first reduction gear unit is provided by a planetary gear in a second speed reducer by a Zykloidentyp so that an eccentric rotational force is applied to the second reduction unit, as well as an engine brake with the same. The coaster is limited, an increase in axial thickness of an engine and achieves an effectively increased reduction ratio, and equipped with a coaster brake motor is limited an increase in the total length thereof due to the translator, with better use of space is achieved.