REDUCTION DEVICE

A reduction device (18) includes a fixed-side housing (19) accommodating a hydraulic motor (12) having an output shaft (16) and a rotating-side housing (21) rotated with respect to the fixed-side housing (19), and a first-stage planetary gear reduction mechanism (24) having a first sun gear (28) and a second-stage planetary gear reduction mechanism (32) having a second sun gear (33) are provided in the rotating-side housing (21). The first-stage planetary gear reduction mechanism (24) has a rotational shaft (25) having one side in an axial direction spline-connected with the output shaft (16), while the first sun gear (28) is provided on the other side in the axial direction of the rotational shaft (25). A small-diameter shaft (27B) is provided on the rotational shaft (25), and first and second half bushes (40, 41) are fitted with the small-diameter shaft (27B) from a radial direction. Thereby, the first sun gear (28) and a stepped part (34A) of the second sun gear (33) are slidably brought into contact with flange parts (40B, 41B) of the first and second half bushes (40, 41).