The present invention provides a reduction device for avoiding phenomenons that the reduction apparatus is disassembled and larger components fall off because of stronger impact, and stifling secondary accidents in the cradle. The reduction apparatus (40) has an input shaft (a crankshaft ) (42) for making an external gear (a planet gear ) ( from 46A to 46C) oscillate and rotate. The input shaft (42) are supported by a first flange body and a second flange body (a wheel carrier body ) (54, 56) through a couple of first angular contact ball bearing and second angular contact ball bearing (50, 52), as bearings of the input shaft (42), the first and second angular contact ball bearings (50, 52) have contact angles (theta 1, theta 2) of approximate 40 DEG and are assembled in a back-to-back combination mode.